API reference

energy(model; numbers..., parameters...)

Return an eigenvalue for a given model.

hermite_polynomial(model, args...; kwargs...)

Evaluate a Hermite polynomial for a given model.

laguerre_polynomial(model, args...; kwargs...)

Evaluate a Laguerre polynomial for a given model.

legendre_polynomial(model, args...; kwargs...)

Evaluate a Rodrigues-form polynomial/function for a given model.

n_max(model)

Return the maximum quantum number for a given model.

potential(model, args...)

Return the potential for a given model.

radial_function(model, args...; kwargs...)

Return a radial function for a given model.

spherical_harmonic(model, args...; kwargs...)

Evaluate a spherical harmonic for a given model.

wavefunction(model, args...; kwargs...)

Return a wavefunction for a given model.

Model

This model is described with the time-independent Schrödinger equation

\[ \hat{H} \psi(x) = E \psi(x),\]

and the Hamiltonian

\[ \hat{H} = - \frac{\hbar^2}{2m} \frac{\mathrm{d}^2}{\mathrm{d}x ^2} - \alpha \delta(x).\]

Parameters are specified with the following struct:

DP = DeltaPotential(alpha=1.0, m=1.0, hbar=1.0)

$\alpha$ is the potential strength, $m$ is the mass of particle and $\hbar$ is the reduced Planck constant (Dirac's constant).

References

• [1] D. J. Griffiths, D. F. Schroeter, Introduction to Quantum Mechanics Third Edition (Cambridge University Press, 2018), (https://doi.org/10.1017/9781316995433) p.63, 2.5.2 The Delta-Function Well
• [2] UCSD Physics 130, Quantum Physics, (https://quantummechanics.ucsd.edu/ph130a/130_notes/node154.html)

energy(model::DeltaPotential)

\[E = - \frac{m\alpha^2}{2\hbar^2}\]

potential(model::DeltaPotential, x)

\[V(x) = -\alpha \delta(x).\]

wavefunction(model::DeltaPotential, x)

\[\psi(x) = \frac{\sqrt{m\alpha}}{\hbar} \mathrm{e}^{-m\alpha |x|/\hbar^2}\]

Model

This model is described with the time-independent Schrödinger equation

\[ \hat{H} \psi(x) = E \psi(x),\]

and the Hamiltonian

\[ \hat{H} = - \frac{\hbar^2}{2m} \frac{\mathrm{d}^2}{\mathrm{d}x ^2} + V(x).\]

Parameters are specified with the following struct:

IPW = InfinitePotentialWell(L=1.0, m=1.0, hbar=1.0)

$L$ is the length of the box, $m$ is the mass of particle and $\hbar$ is the reduced Planck constant (Dirac's constant).

References

• [1] D. J. Griffiths, D. F. Schroeter, Introduction to Quantum Mechanics Third Edition (Cambridge University Press, 2018) (https://doi.org/10.1017/9781316995433) p.31, 2.2 THE INFINITE SQUARE WELL

Proofs

• Eigen Functions & Eigen Values
• Normalization

energy(model::InfinitePotentialWell; n::Integer=1)

\[E_n = \frac{\hbar^2 n^2 \pi^2}{2 m L^2}\]

potential(model::InfinitePotentialWell; x)

\[V(x) = \left\{ \begin{array}{ll} 0 & 0 \leq x \leq L \\ \infty & x \lt 0, L \lt x \end{array} \right.\]

wavefunction(model::InfinitePotentialWell, x; n::Integer=1)

\[\psi_n(x) = \sqrt{\frac{2}{L}} \sin \frac{n\pi x}{L}\]

Model

This model is described with the time-independent Schrödinger equation

\[ \hat{H} \psi(x) = E \psi(x),\]

and the Hamiltonian

\[ \hat{H} = - \frac{\hbar^2}{2m} \frac{\mathrm{d}^2}{\mathrm{d}x ^2} + \frac{1}{2} k x^2.\]

Parameters are specified with the following struct:

HO = HarmonicOscillator(k=1.0, m=1.0, hbar=1.0)

$k$ is the force constant, $m$ is the mass of the particle and $\hbar$ is the reduced Planck constant (Dirac's constant).

References

Main:

• [3] The Digital Library of Mathematical Functions (DLMF) 18.5.18
• [4] C++ Japanese Reference cpprefjp, laguerre_polynomial
• [1] D. J. Griffiths, D. F. Schroeter, Introduction to Quantum Mechanics Third Edition (Cambridge University Press, 2018) p.48, 2.3.2 Analytic Method

Supplemental:

• [3] The Digital Library of Mathematical Functions (DLMF) 18.3 Table1, 18.5 Table1, 18.5.13, 18.5.18
• [5] L. D. Landau, E. M. Lifshitz, Quantum Mechanics (Pergamon Press, 1965) p.595 (a.4), (a.6)
• [6] L. I. Schiff, Quantum Mechanics (McGraw-Hill Book Company, 1968) p.71 (13.12)
• [7] A. Messiah, Quanfum Mechanics (Dover Publications, 1999) p.491 (B.59)
• [8] W. Greiner, Quantum Mechanics: An Introduction Third Edition (Springer, 1994) p.152 (7.22)
• [9] D. J. Griffiths, Introduction to Quantum Mechanics (Prentice Hall, 1995) p.41 Table 2.1, p.43 (2.70)
• [10] D. A. McQuarrie, J. D. Simon, Physical Chemistry: A Molecular Approach (University Science Books, 1997) p.170 Table 5.2
• [11] P. W. Atkins, J. De Paula, Atkins' Physical Chemistry, 8th edition (W. H. Freeman, 2008) p.293 Table 9.1
• [12] J. J. Sakurai, J. Napolitano, Modern Quantum Mechanics Third Edition (Cambridge University Press, 2021) p.524 (B.29)

energy(model::HarmonicOscillator; n::Integer=0)

\[E_n = \hbar \omega \left( n + \frac{1}{2} \right),\]

where $\omega = \sqrt{k/m}$ is the angular frequency.

laguerre_polynomial(model::HarmonicOscillator, x; n=0)

Rodrigues' formula & closed-form:

\[\begin{aligned} H_{n}(x) &:= (-1)^n \mathrm{e}^{x^2} \frac{\mathrm{d}^n}{\mathrm{d}x^n} \mathrm{e}^{-x^2} \\ &= n! \sum_{m=0}^{\lfloor n/2 \rfloor} \frac{(-1)^m}{m! (n-2m)!}(2 x)^{n-2m}. \end{aligned}\]

Examples:

\[\begin{aligned} H_{0}(x) &= 1, \\ H_{1}(x) &= 2 x, \\ H_{2}(x) &= -2 + 4 x^{2}, \\ H_{3}(x) &= -12 x + 8 x^{3}, \\ H_{4}(x) &= 12 - 48 x^{2} + 16 x^{4}, \\ H_{5}(x) &= 120 x - 160 x^{3} + 32 x^{5}, \\ H_{6}(x) &= -120 + 720 x^{2} - 480 x^{4} + 64 x^{6}, \\ H_{7}(x) &= -1680 x + 3360 x^{3} - 1344 x^{5} + 128 x^{7}, \\ H_{8}(x) &= 1680 - 13440 x^{2} + 13440 x^{4} - 3584 x^{6} + 256 x^{8}, \\ H_{9}(x) &= 30240 x - 80640 x^{3} + 48384 x^{5} - 9216 x^{7} + 512 x^{9}, \\ &\vdots \end{aligned}\]

potential(model::HarmonicOscillator, x)

\[V(x) = \frac{1}{2} k x^2 = \frac{1}{2} m \omega^2 x^2 = \frac{1}{2} \hbar \omega \xi^2,\]

where $\omega = \sqrt{k/m}$ is the angular frequency and $\xi = \sqrt{\frac{m\omega}{\hbar}}x$.

wavefunction(model::HarmonicOscillator, x; n::Integer=0)

\[\psi_n(x) = A_n H_n(\xi) \exp{\left( -\frac{\xi^2}{2} \right)},\]

where $\omega = \sqrt{k/m}$, $\xi = \sqrt{\frac{m\omega}{\hbar}}x$, $A_n = \sqrt{\frac{1}{n! 2^n} \sqrt{\frac{m\omega}{\pi\hbar}}}$, $H_n(x) = (-1)^n \mathrm{e}^{x^2} \frac{\mathrm{d}^n}{\mathrm{d}x^n} \mathrm{e}^{-x^2}$ are defined.

Model

This model is described with the time-independent Schrödinger equation

\[ \hat{H} \psi(r) = E \psi(r),\]

and the Hamiltonian

\[ \hat{H} = - \frac{\hbar^2}{2\mu} \frac{\mathrm{d}^2}{\mathrm{d}r ^2} + D_\mathrm{e} \left( \mathrm{e}^{-2a(r-r_e)} - 2\mathrm{e}^{-a(r-r_e)} \right),\]

where $a = \sqrt{\frac{k}{2Dₑ}}$ is defined. Parameters are specified with the following struct:

MP = MorsePotential(r_e=2.0, D_e=0.1, k=0.1, mu=918.1, hbar=1.0)

$r_\mathrm{e}$ is the equilibrium bond distance, $D_\mathrm{e}$ is the the well depth , $k$ is the force constant, $\mu$ is the reduced mass and $\hbar$ is the reduced Planck constant (Dirac's constant).

References

• [13] P. M. Morse, Phys. Rev., 34, 57 (1929), (https://doi.org/10.1103/PhysRev.34.57)
• [14] J. P. Dahl, M. Springborg, J. Chem. Phys., 88, 4535 (1988). (62), (63) (https://doi.org/10.1063/1.453761)
• [15] W. K. Shao, Y. He, J. Pan, J. Nonlinear Sci. Appl., 9, 5, 3388 (2016). (1.6) (http://dx.doi.org/10.22436/jnsa.009.05.124)
• [3] The Digital Library of Mathematical Functions (DLMF) 18.3 Table1, 18.5 Table1, 18.5.12, 18.5.17_5

energy(model::MorsePotential; n::Integer=0, nocheck=false)

\[E_n = - D_\mathrm{e} + \hbar \omega \left( n + \frac{1}{2} \right) - \chi \hbar \omega \left( n + \frac{1}{2} \right)^2,\]

where $\omega = \sqrt{k/µ}$ and $\chi = \frac{\hbar\omega}{4D_\mathrm{e}}$ are defined.

laguerre_polynomial(model::MorsePotential, x; n=0, α=0)

Rodrigues' formula & closed-form:

\[\begin{aligned} L_n^{(\alpha)}(x) &= \frac{x^{-\alpha}e^x}{n!} \frac{d^n}{dx^n}\left(x^{n+\alpha}e^{-x}\right) \\ &= \sum_{k=0}^n(-1)^k \left(\begin{array}{l} n+\alpha \\ n-k \end{array}\right) \frac{x^k}{k !} \\ &= \sum_{k=0}^n(-1)^k \frac{\Gamma(\alpha+n+1)}{\Gamma(\alpha+k+1)\Gamma(n-k+1)} \frac{x^k}{k !}. \end{aligned}\]

Examples:

\[\begin{aligned} L_0^{(0)}(x) &= 1, \\ L_1^{(0)}(x) &= 1 - x, \\ L_1^{(1)}(x) &= 2 - x, \\ L_2^{(0)}(x) &= 1 - 2 x + 1/2 x^{2}, \\ L_2^{(1)}(x) &= 3 - 3 x + 1/2 x^{2}, \\ L_2^{(2)}(x) &= 6 - 4 x + 1/2 x^{2}, \\ L_3^{(0)}(x) &= 1 - 3 x + 3/2 x^{2} - 1/6 x^{3}, \\ L_3^{(1)}(x) &= 4 - 6 x + 2 x^{2} - 1/6 x^{3}, \\ L_3^{(2)}(x) &= 10 - 10 x + 5/2 x^{2} - 1/6 x^{3}, \\ L_3^{(3)}(x) &= 20 - 15 x + 3 x^{2} - 1/6 x^{3}, \\ L_4^{(0)}(x) &= 1 - 4 x + 3 x^{2} - 2/3 x^{3} + 1/24 x^{4}, \\ L_4^{(1)}(x) &= 5 - 10 x + 5 x^{2} - 5/6 x^{3} + 1/24 x^{4}, \\ L_4^{(2)}(x) &= 15 - 20 x + 15/2 x^{2} - 1 x^{3} + 1/24 x^{4}, \\ L_4^{(3)}(x) &= 35 - 35 x + 21/2 x^{2} - 7/6 x^{3} + 1/24 x^{4}, \\ L_4^{(4)}(x) &= 70 - 56 x + 14 x^{2} - 4/3 x^{3} + 1/24 x^{4}, \\ \vdots \end{aligned}\]

n_max(model::MorsePotential)

\[n_\mathrm{max} = \left\lfloor \frac{2 D_e - \omega}{\omega} \right\rfloor,\]

where $\omega = \sqrt{k/µ}$ is defined.

potential(model::MorsePotential, r)

\[V(r) = D_\mathrm{e} \left( \mathrm{e}^{-2a(r-r_e)} - 2\mathrm{e}^{-a(r-r_e)} \right),\]

where $a = \sqrt{\frac{k}{2Dₑ}}$ is defined. The domain is $0\leq r \lt \infty$.

wavefunction(model::MorsePotential, r; n::Integer=0)

\[\psi_n(r) = N_n z^{\lambda-n-1/2} \mathrm{e}^{-z/2} L_n^{(2\lambda-2n-1)}(\xi),\]

$N_n = \sqrt{\frac{n!(2\lambda-2n-1)a}{\Gamma(2\lambda-n)}}$, $\lambda = \frac{\sqrt{2\mu D_\mathrm{e}}}{a\hbar}$, $a = \sqrt{\frac{k}{2Dₑ}}$, $L_n^{(\alpha)}(x) = \frac{x^{-\alpha} \mathrm{e}^x}{n !} \frac{\mathrm{d}^n}{\mathrm{d} x^n}\left(\mathrm{e}^{-x} x^{n+\alpha}\right)$, $\xi := 2\lambda\mathrm{e}^{-a(r-r_e)}$ are defined. The domain is $0\leq r \lt \infty$.

Model

This model is described with the time-independent Schrödinger equation

\[ \hat{H} \psi(x) = E \psi(x),\]

and the Hamiltonian

\[ \hat{H} = - \frac{\hbar^2}{2 m} \frac{\mathrm{d}^2}{\mathrm{d}x ^2} - \frac{\hbar^2}{m x_0^2} \frac{\lambda(\lambda+1)}{2} \frac{1}{\mathrm{cosh}^2(x/x_0)}.\]

After introducing the dimensionless variables

\[ x^\ast \equiv x/x_0,\qquad E^\ast \equiv \frac{\hbar^2}{m x_0^2} E\]

the Schrödinger equation reduces to

\[ \hat{H}^\ast \psi(x^\ast) = E^\ast \psi(x^\ast),\]

with

\[ \hat{H}^\ast = - \frac{1}{2} \frac{\mathrm{d}^2}{\mathrm{d}{x^\ast}^2} - \frac{\lambda(\lambda+1)}{2} \frac{1}{\mathrm{cosh}^2(x^\ast)}.\]

Parameters are specified within the following struct:

PT = PoschlTeller(lambda=1, m=1.0, hbar=1.0, x_0=1.0)

$\lambda$ determines the potential strength. Currently only integer values for $\lambda$ are supported.

References

• [16] G. Pöschl, E. Teller, Zeitschrift für Physik, 83 (3–4), 143 (1933), (https://doi.org/10.1007%2FBF01331132). More general definitions are given as (2a), (2b) or (11)
• [17] S. Flügge, Practical Quantum Mechanics (Springer Berlin Heidelberg, 1999), (https://doi.org/10.1007/978-3-642-61995-3) p.94 Problem 39. Potential hole of modified Poschl-Teller type

energy(model::PoschlTeller; n::Integer=0, nocheck=false)

\[E_n = -\frac{\hbar^2}{m x_0^2}\frac{\mu^2}{2},\]

where $\mu = \mu(n) = n_\mathrm{max}-n+1$, and $n_\mathrm{max} = \left\lfloor \lambda \right\rfloor - 1$.

legendre_polynomial(model::PoschlTeller, x; n=0, m=0)

Associated Legendre polynomials are the associated Legendre functions for integer indices. Here we use the same notation of the associated Legendre functions as in the model HydrogenAtom.

\[\begin{aligned} P_n^m(x) &= \left( 1-x^2 \right)^{m/2} \frac{\mathrm{d}^m}{\mathrm{d}x^m} P_n(x) \\ &= \left( 1-x^2 \right)^{m/2} \frac{\mathrm{d}^m}{\mathrm{d}x^m} \frac{1}{2^n n!} \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left[ \left( x^2-1 \right)^n \right] \\ &= \frac{1}{2^n} (1-x^2)^{m/2} \sum_{j=0}^{\left\lfloor\frac{n-m}{2}\right\rfloor} (-1)^j \frac{(2n-2j)!}{j! (n-j)! (n-2j-m)!} x^{(n-2j-m)}. \end{aligned}\]

n_max(model::PoschlTeller)

\[n_\mathrm{max} = \left\lfloor \lambda \right\rfloor - 1.\]

potential(model::PoschlTeller, x)

\[\begin{aligned} V(x) &= -\frac{\hbar^2}{m x_0^2} \frac{\lambda(\lambda+1)}{2} \mathrm{sech}^2(x/x_0) \\ &= -\frac{\hbar^2}{m x_0^2} \frac{\lambda(\lambda+1)}{2} \frac{1}{\mathrm{cosh}^2(x/x_0)} . \end{aligned}\]

wavefunction(model::PoschlTeller, x; n::Integer=0)

\[\psi_n(x) = \frac{(-1)^μ}{\sqrt{x_0}} P_\lambda^{\mu}(\mathrm{tanh}(x/x_0)) \sqrt{\mu\frac{\Gamma(\lambda-\mu+1)}{\Gamma(\lambda+\mu+1)}},\]

where $\mu = \mu(n) = n_\mathrm{max}-n+1$, and $n_\mathrm{max} = \left\lfloor \lambda \right\rfloor - 1$ and $P_\lambda^{\mu}$ are the associated Legendre functions.

Model

This model is described with the time-independent Schrödinger equation

\[ \hat{H} \psi(\theta,\varphi) = E \psi(\theta,\varphi),\]

and the Hamiltonian

\[\begin{aligned} \hat{H} &= - \frac{\hbar^2}{2\mu} \nabla^2 + V(r), \\ &= - \frac{\hbar^2}{2I} \left[ \frac{1}{\sin\theta} \frac{\partial}{\partial\theta} \left(\sin\theta \frac{\partial}{\partial\theta}\right) + \frac{1}{\sin^2\theta} \frac{\partial^2}{\partial\phi^2} \right], \\ &= \frac{L^2}{2I} \end{aligned}\]

where $I=\mu R^2$ is the moment of intertia, $\mu=\left(\frac{1}{m_1}+\frac{1}{m_2}\right)^{-1}$ is the reduced mass of two particles, $R$ is the distance between the two particles, and $L^2$ is the angular momentum operator. Parameters are specified with the following struct:

RR = RigidRotor(m_1=1.0, m_2=1.0, R=1.0, hbar=1.0)

$m₁$ and $m₂$ are mass of two particles, $R$ is the distance, and $\hbar$ is the reduced Planck constant (Dirac's constant).

References

• [10] D. A. McQuarrie, J. D. Simon, Physical chemistry : a molecular approach (University Science Books, 1997) (https://mitpress.mit.edu/9781940380216/physical-chemistry/) p.173, 5.8 The Energy Levels of a Rigid Rotator Are $E = \hbar^2 J(J+1) / 2I$
• [18] Chemistry Libre Texts, (https://chem.libretexts.org/Bookshelves/PhysicalandTheoreticalChemistryTextbookMaps/PhysicalChemistry(LibreTexts)/05%3ATheHarmonicOscillatorandtheRigidRotor/5.08%3ATheEnergyLevelsofaRigid_Rotor)

energy(model::RigidRotor; l::Integer=0)

\[E_l = \frac{\hbar^2}{2I}l(l+1),\]

where $I=\mu R^2$ is the moment of inertia, $R$ is the distance, and $\mu$ is the reduced mass of the two particles.

legendre_polynomial(model::RigidRotor, x; n=0, m=0)

Rodrigues' formula & closed-form:

\[\begin{aligned} P_n^m(x) &= \left( 1-x^2 \right)^{m/2} \frac{\mathrm{d}^m}{\mathrm{d}x^m} P_n(x) \\ &= \left( 1-x^2 \right)^{m/2} \frac{\mathrm{d}^m}{\mathrm{d}x^m} \frac{1}{2^n n!} \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left[ \left( x^2-1 \right)^n \right] \\ &= \frac{1}{2^n} (1-x^2)^{m/2} \sum_{j=0}^{\left\lfloor\frac{n-m}{2}\right\rfloor} (-1)^j \frac{(2n-2j)!}{j! (n-j)! (n-2j-m)!} x^{(n-2j-m)}. \end{aligned},\]

where Legendre polynomials are defined as $P_n(x) = \frac{1}{2^n n!} \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left[ \left( x^2-1 \right)^n \right]$. Note that $P_l^{-m} = (-1)^m \frac{(l-m)!}{(l+m)!} P_l^m$ for $m<0$. (It is not compatible with $P_k^m(t) = (-1)^m\left( 1-t^2 \right)^{m/2} \frac{\mathrm{d}^m P_k(t)}{\mathrm{d}t^m}$ caused by $(-1)^m$.) The specific formulae are given below.

Examples:

\[\begin{aligned} P_{0}^{0}(x) &= 1, \\ P_{1}^{0}(x) &= x, \\ P_{1}^{1}(x) &= \left(+1\right)\sqrt{1-x^2}, \\ P_{2}^{0}(x) &= -1/2 + 3/2 x^{2}, \\ P_{2}^{1}(x) &= \left(-3 x\right)\sqrt{1-x^2}, \\ P_{2}^{2}(x) &= 3 - 6 x, \\ P_{3}^{0}(x) &= -3/2 x + 5/2 x^{3}, \\ P_{3}^{1}(x) &= \left(3/2 - 15/2 x^{2}\right)\sqrt{1-x^2}, \\ P_{3}^{2}(x) &= 15 x - 30 x^{2}, \\ P_{3}^{3}(x) &= \left(15 - 30 x\right)\sqrt{1-x^2}, \\ P_{4}^{0}(x) &= 3/8 - 15/4 x^{2} + 35/8 x^{4}, \\ P_{4}^{1}(x) &= \left(- 15/2 x + 35/2 x^{3}\right)\sqrt{1-x^2}, \\ P_{4}^{2}(x) &= -15/2 + 15 x + 105/2 x^{2} - 105 x^{3}, \\ P_{4}^{3}(x) &= \left(105 x - 210 x^{2}\right)\sqrt{1-x^2}, \\ P_{4}^{4}(x) &= 105 - 420 x + 420 x^{2}, \\ & \vdots \end{aligned}\]

potential(model::RigidRotor, r)

\[\begin{aligned} V(r) &= 0, \end{aligned}\]

spherical_harmonic(model::RigidRotor, θ, φ; l=0, m=0)

\[Y_{lm}(\theta,\varphi) = (-1)^{\frac{|m|+m}{2}} \sqrt{\frac{2l+1}{4\pi} \frac{(l-|m|)!}{(l+|m|)!}} P_l^{|m|} (\cos\theta) \mathrm{e}^{im\varphi}.\]

The domain is $0\leq \theta \lt \pi, 0\leq \varphi \lt 2\pi$. Note that some variants are connected by

\[i^{|m|+m} \sqrt{\frac{(l-|m|)!}{(l+|m|)!}} P_l^{|m|} = (-1)^{\frac{|m|+m}{2}} \sqrt{\frac{(l-|m|)!}{(l+|m|)!}} P_l^{|m|} = (-1)^m \sqrt{\frac{(l-m)!}{(l+m)!}} P_l^{m}.\]

wavefunction(model::RigidRotor, θ, φ; l::Integer=0, m::Integer=0)

\[\psi_{lm}(\theta,\varphi) = Y_{lm}(\theta,\varphi)\]

The wave functions are the spherical harmonics. The domain is $0\leq \theta \lt \pi$ and $0\leq \varphi \lt 2\pi$.

Model

This model is described with the time-independent Schrödinger equation

\[ \hat{H} \psi(x,y,z) = E \psi(x,y,z),\]

and the Hamiltonian

\[ \hat{H} = - \frac{\hbar^2}{2m} \left(\frac{\partial^2}{\partial x ^2} + \frac{\partial^2}{\partial y ^2} + \frac{\partial^2}{\partial z ^2}\right) + V(x,y,z).\]

Parameters are specified with the following struct:

IPW3D = InfinitePotentialWell3D(L=[1.0,1.0,1.0], m=1.0, hbar=1.0)

$L$ is a vector of the lengths of the box in $x$,$y$,$z$-direction, $m$ is the mass of the particle and $\hbar$ is the reduced Planck constant (Dirac's constant).

References

• [10] D. A. McQuarrie, J. D. Simon, Physical chemistry : a molecular approach (University Science Books, 1997), (https://mitpress.mit.edu/9781940380216/physical-chemistry/) p.90, 3-9. The Problem of a Particle in a Three-Dimensional Box Is a Simple Extension of the One-Dimensional Case

energy(model::InfinitePotentialWell3D; n::Vector{Int}=[1,1,1])

\[E_{n_x,n_y,n_z} = \frac{\hbar^2 n_x^2 \pi^2}{2 m L_x^2} + \frac{\hbar^2 n_y^2 \pi^2}{2 m L_y^2} + \frac{\hbar^2 n_z^2 \pi^2}{2 m L_z^2}\]

potential(model::InfinitePotentialWell3D, x)

\[V(x,y,z) = \left\{ \begin{array}{ll} 0 & 0 \leq x \leq L_x \ \mathrm{and}\ 0 \leq y \leq L_y \ \mathrm{and}\ 0 \leq z \leq L_z \\ \infty & \mathrm{elsewhere} \end{array} \right.\]

wavefunction(model::InfinitePotentialWell3D, x; n::Vector{Int}=[1,1,1])

The wave functions can be expressed as products of wave functions in a one-dimensional box.

\[\begin{aligned} \psi_{n_x,n_y,n_z}(x,y,z) &= \psi_{n_x}(x) \times \psi_{n_y}(y) \times \psi_{n_z}(z) \\ &= \sqrt{\frac{2}{L_x}} \sin \frac{n_x \pi x}{L_x} \times \sqrt{\frac{2}{L_y}} \sin \frac{n_y \pi y}{L_y} \times \sqrt{\frac{2}{L_z}} \sin \frac{n_z \pi z}{L_z} \end{aligned}\]

Model

This model is described with the time-independent Schrödinger equation

\[ \hat{H} \psi(\pmb{r}) = E \psi(\pmb{r}),\]

and the Hamiltonian

\[ \hat{H} = - \frac{\hbar^2}{2\mu} \nabla^2 + \frac{1}{2} k r^2.\]

Parameters are specified with the following struct:

SO = SphericalOscillator(k=1.0, mu=1.0, hbar=1.0)

$k$ is the force constant, $μ$ is the mass of particle and $\hbar$ is the reduced Planck constant (Dirac's constant).

References

• [17] S. Flügge, Practical Quantum Mechanics (Springer Berlin Heidelberg, 1999), (https://doi.org/10.1007/978-3-642-61995-3) [p.166, Problem 65. Spherical oscillator].
• [19] UCSD Physics 130, Quantum Physics, (https://quantummechanics.ucsd.edu/ph130a/130_notes/node244.html)

energy(model::SphericalOscillator; n::Integer=0, l::Integer=0)

\[E_{nl} = \left(2n + l + \frac{3}{2}\right)\hbar \omega,\]

where $\omega = \sqrt{k/\mu}$.

laguerre_polynomial(model::SphericalOscillator, x; n=0, α=0)

Rodrigues' formula & closed-form:

\[\begin{aligned} L_n^{(\alpha)}(x) &= \frac{x^{-\alpha}e^x}{n!} \frac{d^n}{dx^n}\left(x^{n+\alpha}e^{-x}\right) \\ &= \sum_{k=0}^n(-1)^k \left(\begin{array}{l} n+\alpha \\ n-k \end{array}\right) \frac{x^k}{k !} \\ &= \sum_{k=0}^n(-1)^k \frac{\Gamma(\alpha+n+1)}{\Gamma(\alpha+k+1)\Gamma(n-k+1)} \frac{x^k}{k !}. \end{aligned}\]

Examples:

\[\begin{aligned} L_0^{(0)}(x) &= 1, \\ L_1^{(0)}(x) &= 1 - x, \\ L_1^{(1)}(x) &= 2 - x, \\ L_2^{(0)}(x) &= 1 - 2 x + 1/2 x^{2}, \\ L_2^{(1)}(x) &= 3 - 3 x + 1/2 x^{2}, \\ L_2^{(2)}(x) &= 6 - 4 x + 1/2 x^{2}, \\ L_3^{(0)}(x) &= 1 - 3 x + 3/2 x^{2} - 1/6 x^{3}, \\ L_3^{(1)}(x) &= 4 - 6 x + 2 x^{2} - 1/6 x^{3}, \\ L_3^{(2)}(x) &= 10 - 10 x + 5/2 x^{2} - 1/6 x^{3}, \\ L_3^{(3)}(x) &= 20 - 15 x + 3 x^{2} - 1/6 x^{3}, \\ L_4^{(0)}(x) &= 1 - 4 x + 3 x^{2} - 2/3 x^{3} + 1/24 x^{4}, \\ L_4^{(1)}(x) &= 5 - 10 x + 5 x^{2} - 5/6 x^{3} + 1/24 x^{4}, \\ L_4^{(2)}(x) &= 15 - 20 x + 15/2 x^{2} - 1 x^{3} + 1/24 x^{4}, \\ L_4^{(3)}(x) &= 35 - 35 x + 21/2 x^{2} - 7/6 x^{3} + 1/24 x^{4}, \\ L_4^{(4)}(x) &= 70 - 56 x + 14 x^{2} - 4/3 x^{3} + 1/24 x^{4}, \\ \vdots \end{aligned}\]

legendre_polynomial(model::SphericalOscillator, x; n=0, m=0)

Rodrigues' formula & closed-form:

\[\begin{aligned} P_n^m(x) &= \left( 1-x^2 \right)^{m/2} \frac{\mathrm{d}^m}{\mathrm{d}x^m} P_n(x) \\ &= \left( 1-x^2 \right)^{m/2} \frac{\mathrm{d}^m}{\mathrm{d}x^m} \frac{1}{2^n n!} \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left[ \left( x^2-1 \right)^n \right] \\ &= \frac{1}{2^n} (1-x^2)^{m/2} \sum_{j=0}^{\left\lfloor\frac{n-m}{2}\right\rfloor} (-1)^j \frac{(2n-2j)!}{j! (n-j)! (n-2j-m)!} x^{(n-2j-m)}. \end{aligned},\]

where Legendre polynomials are defined as $P_n(x) = \frac{1}{2^n n!} \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left[ \left( x^2-1 \right)^n \right]$. Note that $P_l^{-m} = (-1)^m \frac{(l-m)!}{(l+m)!} P_l^m$ for $m<0$. (It is not compatible with $P_k^m(t) = (-1)^m\left( 1-t^2 \right)^{m/2} \frac{\mathrm{d}^m P_k(t)}{\mathrm{d}t^m}$ caused by $(-1)^m$.) The specific formulae are given below.

Examples:

\[\begin{aligned} P_{0}^{0}(x) &= 1, \\ P_{1}^{0}(x) &= x, \\ P_{1}^{1}(x) &= \left(+1\right)\sqrt{1-x^2}, \\ P_{2}^{0}(x) &= -1/2 + 3/2 x^{2}, \\ P_{2}^{1}(x) &= \left(-3 x\right)\sqrt{1-x^2}, \\ P_{2}^{2}(x) &= 3 - 6 x, \\ P_{3}^{0}(x) &= -3/2 x + 5/2 x^{3}, \\ P_{3}^{1}(x) &= \left(3/2 - 15/2 x^{2}\right)\sqrt{1-x^2}, \\ P_{3}^{2}(x) &= 15 x - 30 x^{2}, \\ P_{3}^{3}(x) &= \left(15 - 30 x\right)\sqrt{1-x^2}, \\ P_{4}^{0}(x) &= 3/8 - 15/4 x^{2} + 35/8 x^{4}, \\ P_{4}^{1}(x) &= \left(- 15/2 x + 35/2 x^{3}\right)\sqrt{1-x^2}, \\ P_{4}^{2}(x) &= -15/2 + 15 x + 105/2 x^{2} - 105 x^{3}, \\ P_{4}^{3}(x) &= \left(105 x - 210 x^{2}\right)\sqrt{1-x^2}, \\ P_{4}^{4}(x) &= 105 - 420 x + 420 x^{2}, \\ & \vdots \end{aligned}\]

potential(model::SphericalOscillator, r)

\[V(r) = \frac{1}{2} k r^2 = \frac{1}{2} \mu \omega^2 r^2 = \frac{1}{2} \hbar \omega \xi^2,\]

where $\omega = \sqrt{k/\mu}$ is the angular frequency and $\xi = \sqrt{\frac{\mu\omega}{\hbar}}r$.

radial_function(model::SphericalOscillator, r; n=0, l=0)

\[R_{nl}(r) = \sqrt{ \frac{\gamma^{3/2}}{2\sqrt{\pi}}} \sqrt{\frac{2^{n+l+3} n!}{(2n+2l+1)!!}} \xi^l \exp\left(-\xi^2/2\right)L_{n}^{(l+\frac{1}{2})} \left(\xi^2\right),\]

where $\gamma = \mu\omega/\hbar$ and $\xi = \sqrt{\gamma}r = \sqrt{\mu\omega/\hbar}r$ are defined. The generalized Laguerre polynomials are defined as $L_n^{(\alpha)}(x) = \frac{x^{-\alpha} \mathrm{e}^x}{n !} \frac{\mathrm{d}^n}{\mathrm{d} x^n}\left(\mathrm{e}^{-x} x^{n+\alpha}\right)$. The domain is $0\leq r \lt \infty$.

spherical_harmonic(model::SphericalOscillator, θ, φ; l=0, m=0)

\[Y_{lm}(\theta,\varphi) = (-1)^{\frac{|m|+m}{2}} \sqrt{\frac{2l+1}{4\pi} \frac{(l-|m|)!}{(l+|m|)!}} P_l^{|m|} (\cos\theta) \mathrm{e}^{im\varphi}.\]

The domain is $0\leq \theta \lt \pi, 0\leq \varphi \lt 2\pi$. Note that some variants are connected by

\[i^{|m|+m} \sqrt{\frac{(l-|m|)!}{(l+|m|)!}} P_l^{|m|} = (-1)^{\frac{|m|+m}{2}} \sqrt{\frac{(l-|m|)!}{(l+|m|)!}} P_l^{|m|} = (-1)^m \sqrt{\frac{(l-m)!}{(l+m)!}} P_l^{m}.\]

wavefunction(model::SphericalOscillator, r, θ, φ; n::Integer=0, l::Integer=0, m::Integer=0)

\[\psi_{nlm}(\pmb{r}) = R_{nl}(r) Y_{lm}(\theta,\varphi)\]

The domain is $0\leq r \lt \infty, 0\leq \theta \lt \pi, 0\leq \varphi \lt 2\pi$.

Model

This model is described with the time-independent Schrödinger equation

\[ \hat{H} \psi(\pmb{r}) = E \psi(\pmb{r}),\]

and the Hamiltonian

\[ \hat{H} = - \frac{\hbar^2}{2\mu} \nabla^2 - \frac{Z}{r/a_0} E_\mathrm{h},\]

where $\mu=\left(\frac{1}{m_\mathrm{e}}+\frac{1}{m_\mathrm{p}}\right)^{-1}$ is the reduced mass of electron $\mathrm{e}$ and proton $\mathrm{p}$. $\mu = m_\mathrm{e}$ holds in the limit $m_\mathrm{p}\rightarrow\infty$. The potential includes only Coulomb interaction and it does not include fine or hyperfine interactions in this model. Parameters are specified with the following struct:

HA = HydrogenAtom(Z=1, m_e=1.0, a_0=1.0, E_h=1.0, hbar=1.0)

$Z$ is the atomic number, $m_\mathrm{e}$ is the electron mass, $a_0$ is the Bohr radius, $E_\mathrm{h}$ is the Hartree energy and $\hbar$ is the reduced Planck constant (Dirac's constant).

References

Main:

• [3] The Digital Library of Mathematical Functions (DLMF), 18.3 Table1, 18.5 Table1, 18.5.16, 18.5.17
• [4] C++ Japanese Reference cpprefjp, assoc_legendre, assoc_laguerre
• [20] A. Messiah, Quantum Mechanics VOLUME Ⅰ (North-Holland Publishing Company, 1961), p.412 (XI.3), p.419 (XI.18) (XI.18a) (XI.18b), p.483 (B.12), p.493 (B.71) (B.72), p.494 (B.81), p495 (B.93)

Supplemental:

• [4] C++ Japanese Reference legendre, assoc_legendre, laguerre_polynomial, assoc_laguerre
• [3] The Digital Library of Mathematical Functions (DLMF), 18.3 Table1, 18.5 Table1, 18.5.16, 18.5.17, 18.5.12
• [5] L. D. Landau, E. M. Lifshitz, Quantum Mechanics (Pergamon Press, 1965), p.598 (c.1), p.598 (c.4), p.603 (d.13)
• [6] L. I. Schiff, Quantum Mechanics (McGraw-Hill Book Company, 1968), p.79 (14.12), p.93 (16.19)
• [7] A. Messiah, Quanfum Mechanics (Dover Publications, 1999), p.493 (B.72), p.494 Table, p.493 (B.72), p.483 (B.12), p.483 (B.１２)
• [9] D. J. Griffiths, Introduction to Quantum Mechanics (Prentice Hall, 1995), p.126 (4.28), p.96 Table3.1, p.126 (4.27), p.139 (4.88), p.140 Table4.4, p.139 (4.87), p.140 Table4.5
• [10] D. A. McQuarrie, J. D. Simon, Physical Chemistry: A Molecular Approach (University Science Books, 1997), p.195 Table6.1, p.196 (6.26), p.196 Table6.2, p.207 Table6.4
• [11] P. W. Atkins, J. De Paula, Atkins' Physical Chemistry, 8th edition (W. H. Freeman, 2008), p.234
• [12] J. J. Sakurai, J. Napolitano, Modern Quantum Mechanics Third Edition (Cambridge University Press, 2021), p.245 Problem 3.30.b

energy(model::HydrogenAtom; n::Integer=1)

\[E_n = -\frac{m_\mathrm{e} e^4 Z^2}{2n^2(4\pi\varepsilon_0)^2\hbar^2} = -\frac{Z^2}{2n^2} E_\mathrm{h},\]

where $E_\mathrm{h} = \frac{\hbar^2}{m_\mathrm{e}{a_0}^2} = \frac{e^2}{4\pi\varepsilon_0a_0} = \frac{m_\mathrm{e}e^4}{\left(4\pi\varepsilon_0\right)^2\hbar^2}$ is the Hartree energy, one of atomic unit. About atomic units, see section 3.9.2 of the IUPAC GreenBook. In other units, $E_\mathrm{h} = 27.211~386~245~988(53)~\mathrm{eV}$ from here.

laguerre_polynomial(model::HydrogenAtom, x; n=0, k=0)

Rodrigues' formula & closed-form:

\[\begin{aligned} L_n^{k}(x) &= \frac{\mathrm{d}^k}{\mathrm{d}x^k} L_n(x) \\ &= \frac{\mathrm{d}^k}{\mathrm{d}x^k} \frac{1}{n!} \mathrm{e}^x \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left( \mathrm{e}^{-x} x^n \right) \\ &= \sum_{m=0}^{n-k} (-1)^{m+k} \frac{n!}{m!(m+k)!(n-m-k)!} x^m \\ &= (-1)^k L_{n-k}^{(k)}(x), \end{aligned}\]

where Laguerre polynomials are defined as $L_n(x)=\frac{1}{n!}\mathrm{e}^x \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left( \mathrm{e}^{-x} x^n \right)$.

Examples:

\[\begin{aligned} L_0^0(x) &= 1, \\ L_1^0(x) &= 1 - x, \\ L_1^1(x) &= 1, \\ L_2^0(x) &= 1 - 2 x + 1/2 x^2, \\ L_2^1(x) &= 2 - x, \\ L_2^2(x) &= 1, \\ L_3^0(x) &= 1 - 3 x + 3/2 x^2 - 1/6 x^3, \\ L_3^1(x) &= 3 - 3 x + 1/2 x^2, \\ L_3^2(x) &= 3 - x, \\ L_3^3(x) &= 1, \\ L_4^0(x) &= 1 - 4 x + 3 x^2 - 2/3 x^3 + 5/12 x^4, \\ L_4^1(x) &= 4 - 6 x + 2 x^2 - 1/6 x^3, \\ L_4^2(x) &= 6 - 4 x + 1/2 x^2, \\ L_4^3(x) &= 4 - x, \\ L_4^4(x) &= 1, \\ \vdots \end{aligned}\]

legendre_polynomial(model::HydrogenAtom, x; n=0, m=0)

Rodrigues' formula & closed-form:

\[\begin{aligned} P_n^m(x) &= \left( 1-x^2 \right)^{m/2} \frac{\mathrm{d}^m}{\mathrm{d}x^m} P_n(x) \\ &= \left( 1-x^2 \right)^{m/2} \frac{\mathrm{d}^m}{\mathrm{d}x^m} \frac{1}{2^n n!} \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left[ \left( x^2-1 \right)^n \right] \\ &= \frac{1}{2^n} (1-x^2)^{m/2} \sum_{j=0}^{\left\lfloor\frac{n-m}{2}\right\rfloor} (-1)^j \frac{(2n-2j)!}{j! (n-j)! (n-2j-m)!} x^{(n-2j-m)}. \end{aligned},\]

where Legendre polynomials are defined as $P_n(x) = \frac{1}{2^n n!} \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left[ \left( x^2-1 \right)^n \right]$. Note that $P_l^{-m} = (-1)^m \frac{(l-m)!}{(l+m)!} P_l^m$ for $m<0$. (It is not compatible with $P_k^m(t) = (-1)^m\left( 1-t^2 \right)^{m/2} \frac{\mathrm{d}^m P_k(t)}{\mathrm{d}t^m}$ caused by $(-1)^m$.) The specific formulae are given below.

Examples:

\[\begin{aligned} P_{0}^{0}(x) &= 1, \\ P_{1}^{0}(x) &= x, \\ P_{1}^{1}(x) &= \left(+1\right)\sqrt{1-x^2}, \\ P_{2}^{0}(x) &= -1/2 + 3/2 x^{2}, \\ P_{2}^{1}(x) &= \left(-3 x\right)\sqrt{1-x^2}, \\ P_{2}^{2}(x) &= 3 - 6 x, \\ P_{3}^{0}(x) &= -3/2 x + 5/2 x^{3}, \\ P_{3}^{1}(x) &= \left(3/2 - 15/2 x^{2}\right)\sqrt{1-x^2}, \\ P_{3}^{2}(x) &= 15 x - 30 x^{2}, \\ P_{3}^{3}(x) &= \left(15 - 30 x\right)\sqrt{1-x^2}, \\ P_{4}^{0}(x) &= 3/8 - 15/4 x^{2} + 35/8 x^{4}, \\ P_{4}^{1}(x) &= \left(- 15/2 x + 35/2 x^{3}\right)\sqrt{1-x^2}, \\ P_{4}^{2}(x) &= -15/2 + 15 x + 105/2 x^{2} - 105 x^{3}, \\ P_{4}^{3}(x) &= \left(105 x - 210 x^{2}\right)\sqrt{1-x^2}, \\ P_{4}^{4}(x) &= 105 - 420 x + 420 x^{2}, \\ & \vdots \end{aligned}\]

potential(model::HydrogenAtom, r)

\[\begin{aligned} V(r) &= - \frac{Ze^2}{4\pi\varepsilon_0 r} &= - \frac{e^2}{4\pi\varepsilon_0 a_0} \frac{Z}{r/a_0} &= - \frac{Z}{r/a_0} E_\mathrm{h}, \end{aligned}\]

where $E_\mathrm{h} = \frac{\hbar^2}{m_\mathrm{e}{a_0}^2} = \frac{e^2}{4\pi\varepsilon_0a_0} = \frac{m_\mathrm{e}e^4}{\left(4\pi\varepsilon_0\right)^2\hbar^2}$ is the Hartree energy, one of atomic unit. The domain is $0\leq r \lt \infty$.

radial_function(model::HydrogenAtom, r; n=1, l=0)

\[R_{nl}(r) = -\sqrt{\frac{(n-l-1)!}{2n(n+l)!} \left(\frac{2Z}{n a_0}\right)^3} \left(\frac{2Zr}{n a_0}\right)^l \exp \left(-\frac{Zr}{n a_0}\right) L_{n+l}^{2l+1} \left(\frac{2Zr}{n a_0}\right),\]

where the Laguerre polynomials are defined as $L_n(x) = \frac{1}{n!} \mathrm{e}^x \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left( \mathrm{e}^{-x} x^n \right)$, and the associated Laguerre polynomials are defined as $L_n^{k}(x) = \frac{\mathrm{d}^k}{\mathrm{d}x^k} L_n(x)$. Note that replace $2n(n+l)!$ with $2n[(n+l)!]^3$ if the Laguerre polynomials are defined as $L_n(x) = \mathrm{e}^x \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left( \mathrm{e}^{-x} x^n \right)$. Note that replace $L_{n+l}^{2l+1}(x)$ with $- L_{n-l-1}^{2l+1}(x)$ if the associated Laguerre polynomials are defined as $L_n^{k}(x) = (-1)^k \frac{\mathrm{d}^k}{\mathrm{d}x^k} L_{n+k}(x)$, which we call the generalized Laguerre polynomials. The domain is $0\leq r \lt \infty$.

spherical_harmonic(model::HydrogenAtom, θ, φ; l=0, m=0)

\[Y_{lm}(\theta,\varphi) = (-1)^{\frac{|m|+m}{2}} \sqrt{\frac{2l+1}{4\pi} \frac{(l-|m|)!}{(l+|m|)!}} P_l^{|m|} (\cos\theta) \mathrm{e}^{im\varphi}.\]

The domain is $0\leq \theta \lt \pi, 0\leq \varphi \lt 2\pi$. Note that some variants are connected by

\[i^{|m|+m} \sqrt{\frac{(l-|m|)!}{(l+|m|)!}} P_l^{|m|} = (-1)^{\frac{|m|+m}{2}} \sqrt{\frac{(l-|m|)!}{(l+|m|)!}} P_l^{|m|} = (-1)^m \sqrt{\frac{(l-m)!}{(l+m)!}} P_l^{m}.\]

wavefunction(model::HydrogenAtom, r, θ, φ; n::Integer=1, l::Integer=0, m::Integer=0)

\[\psi_{nlm}(\pmb{r}) = R_{nl}(r) Y_{lm}(\theta,\varphi)\]

The domain is $0\leq r \lt \infty, 0\leq \theta \lt \pi, 0\leq \varphi \lt 2\pi$.

Model

This model is described with the time-independent Schrödinger equation

\[ \hat{H} \psi(\pmb{r}) = E \psi(\pmb{r}),\]

and the Hamiltonian

\[ \hat{H} = - \frac{\hbar^2}{2\mu} \nabla^2 + \frac{z_1 z_2}{r/a_0} E_\mathrm{h},\]

where $\mu=\left(\frac{1}{m_1}+\frac{1}{m_2}\right)^{-1}$ is the reduced mass of particle 1 and particle 2. The potential includes only Coulomb interaction and it does not include fine or hyperfine interactions in this model. Parameters are specified with the following struct:

CTB = CoulombTwoBody(z_1=-1, z_2=1, m_1=1.0, m_2=1.0, m_e=1.0, a_0=1.0, E_h=1.0, hbar=1.0)

$z₁$ is the charge number of particle 1, $z₂$ is the charge number of particle 2, $m₁$ is the mass of particle 1, $m₂$ is the mass of particle 2, $m_\mathrm{e}$ is the electron mass (use the same unit as $m₁$ and $m₂$. For example of hydrogen atom, use $m_\mathrm{e}=9.1093837139\times10^{-31}\mathrm{kg}$, $m_1=9.1093837139\times10^{-31}\mathrm{kg}$ and $m_2=1.67262192595\times10^{-27}\mathrm{kg}$ in the IS unit system, use $~m_\mathrm{e}=1.0~m_\mathrm{e}$, $m_1=1.0~m_\mathrm{e}$ and $m_2=1836.152673426~m_\mathrm{e}$ in the atomic unit.), $a_0$ is the Bohr radius, $E_\mathrm{h}$ is the Hartree energy and $\hbar$ is the reduced Planck constant (Dirac's constant).

References

• [3] The Digital Library of Mathematical Functions (DLMF), 18.3 Table1, 18.5 Table1, 18.5.16, 18.5.17
• [4] C++ Japanese Reference (C++日本語リファレンス) cpprefjp, assoc_legendre, assoc_laguerre
• [20] A. Messiah, Quantum Mechanics VOLUME Ⅰ (North-Holland Publishing Company, 1961), p.412 I. THE HYDROGEN ATOM
• [1] D. J. Griffiths, D. F. Schroeter, Introduction to Quantum Mechanics Third Edition (Cambridge University Press, 2018) (https://doi.org/10.1017/9781316995433) p.143 4.2 THE HYDROGEN ATOM, p.200 Problem 5.1, p.200 Problem 5.2
• [21] W. Greiner, Quantum Mechanics: An Introduction Forth Edition (Springer, 2001) (https://doi.org/10.1007/978-3-642-56826-8) p.217 The Hydrogen Atom, p.236 9.5 Spectrum of a Diatomic Molecule

energy(model::CoulombTwoBody; n::Integer=1)

\[E_n = -\frac{(z_1 z_2)^2}{2n^2} \frac{\mu}{m_\mathrm{e}} E_\mathrm{h},\]

where $\mu=\left(\frac{1}{m_1}+\frac{1}{m_2}\right)^{-1}$ is the reduced mass of particle 1 and particle 2, $E_\mathrm{h} = \frac{\hbar^2}{m_\mathrm{e}{a_0}^2} = \frac{e^2}{4\pi\varepsilon_0a_0} = \frac{m_\mathrm{e}e^4}{\left(4\pi\varepsilon_0\right)^2\hbar^2}$ is the Hartree energy, one of atomic unit. About atomic units, see section 3.9.2 of the IUPAC GreenBook. In other units, $E_\mathrm{h} = 27.211~386~245~988(53)~\mathrm{eV}$ from here.

laguerre_polynomial(model::CoulombTwoBody, x; n=0, k=0)

Rodrigues' formula & closed-form:

\[\begin{aligned} L_n^{k}(x) &= \frac{\mathrm{d}^k}{\mathrm{d}x^k} L_n(x) \\ &= \frac{\mathrm{d}^k}{\mathrm{d}x^k} \frac{1}{n!} \mathrm{e}^x \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left( \mathrm{e}^{-x} x^n \right) \\ &= \sum_{m=0}^{n-k} (-1)^{m+k} \frac{n!}{m!(m+k)!(n-m-k)!} x^m \\ &= (-1)^k L_{n-k}^{(k)}(x), \end{aligned}\]

where Laguerre polynomials are defined as $L_n(x)=\frac{1}{n!}\mathrm{e}^x \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left( \mathrm{e}^{-x} x^n \right)$.

Examples:

\[\begin{aligned} L_0^0(x) &= 1, \\ L_1^0(x) &= 1 - x, \\ L_1^1(x) &= 1, \\ L_2^0(x) &= 1 - 2 x + 1/2 x^2, \\ L_2^1(x) &= 2 - x, \\ L_2^2(x) &= 1, \\ L_3^0(x) &= 1 - 3 x + 3/2 x^2 - 1/6 x^3, \\ L_3^1(x) &= 3 - 3 x + 1/2 x^2, \\ L_3^2(x) &= 3 - x, \\ L_3^3(x) &= 1, \\ L_4^0(x) &= 1 - 4 x + 3 x^2 - 2/3 x^3 + 5/12 x^4, \\ L_4^1(x) &= 4 - 6 x + 2 x^2 - 1/6 x^3, \\ L_4^2(x) &= 6 - 4 x + 1/2 x^2, \\ L_4^3(x) &= 4 - x, \\ L_4^4(x) &= 1, \\ \vdots \end{aligned}\]

legendre_polynomial(model::CoulombTwoBody, x; n=0, m=0)

Rodrigues' formula & closed-form:

\[\begin{aligned} P_n^m(x) &= \left( 1-x^2 \right)^{m/2} \frac{\mathrm{d}^m}{\mathrm{d}x^m} P_n(x) \\ &= \left( 1-x^2 \right)^{m/2} \frac{\mathrm{d}^m}{\mathrm{d}x^m} \frac{1}{2^n n!} \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left[ \left( x^2-1 \right)^n \right] \\ &= \frac{1}{2^n} (1-x^2)^{m/2} \sum_{j=0}^{\left\lfloor\frac{n-m}{2}\right\rfloor} (-1)^j \frac{(2n-2j)!}{j! (n-j)! (n-2j-m)!} x^{(n-2j-m)}. \end{aligned},\]

where Legendre polynomials are defined as $P_n(x) = \frac{1}{2^n n!} \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left[ \left( x^2-1 \right)^n \right]$. Note that $P_l^{-m} = (-1)^m \frac{(l-m)!}{(l+m)!} P_l^m$ for $m<0$. (It is not compatible with $P_k^m(t) = (-1)^m\left( 1-t^2 \right)^{m/2} \frac{\mathrm{d}^m P_k(t)}{\mathrm{d}t^m}$ caused by $(-1)^m$.) The specific formulae are given below.

Examples:

\[\begin{aligned} P_{0}^{0}(x) &= 1, \\ P_{1}^{0}(x) &= x, \\ P_{1}^{1}(x) &= \left(+1\right)\sqrt{1-x^2}, \\ P_{2}^{0}(x) &= -1/2 + 3/2 x^{2}, \\ P_{2}^{1}(x) &= \left(-3 x\right)\sqrt{1-x^2}, \\ P_{2}^{2}(x) &= 3 - 6 x, \\ P_{3}^{0}(x) &= -3/2 x + 5/2 x^{3}, \\ P_{3}^{1}(x) &= \left(3/2 - 15/2 x^{2}\right)\sqrt{1-x^2}, \\ P_{3}^{2}(x) &= 15 x - 30 x^{2}, \\ P_{3}^{3}(x) &= \left(15 - 30 x\right)\sqrt{1-x^2}, \\ P_{4}^{0}(x) &= 3/8 - 15/4 x^{2} + 35/8 x^{4}, \\ P_{4}^{1}(x) &= \left(- 15/2 x + 35/2 x^{3}\right)\sqrt{1-x^2}, \\ P_{4}^{2}(x) &= -15/2 + 15 x + 105/2 x^{2} - 105 x^{3}, \\ P_{4}^{3}(x) &= \left(105 x - 210 x^{2}\right)\sqrt{1-x^2}, \\ P_{4}^{4}(x) &= 105 - 420 x + 420 x^{2}, \\ & \vdots \end{aligned}\]

potential(model::CoulombTwoBody, r)

\[\begin{aligned} V(r) &= - \frac{z_1 z_2 e^2}{4\pi\varepsilon_0 r} &= - \frac{e^2}{4\pi\varepsilon_0 a_0} \frac{z_1 z_2}{r/a_0} &= - \frac{z_1 z_2}{r/a_0} E_\mathrm{h}, \end{aligned}\]

where $E_\mathrm{h} = \frac{\hbar^2}{m_\mathrm{e}{a_0}^2} = \frac{e^2}{4\pi\varepsilon_0a_0} = \frac{m_\mathrm{e}e^4}{\left(4\pi\varepsilon_0\right)^2\hbar^2}$ is the Hartree energy, one of atomic unit. The domain is $0\leq r \lt \infty$.

radial_function(model::CoulombTwoBody, r; n=1, l=0)

\[R_{nl}(r) = -\sqrt{\frac{(n-l-1)!}{2n(n+l)!} \left(\frac{2Z}{n a_\mu}\right)^3} \left(\frac{2Zr}{n a_\mu}\right)^l \exp \left(-\frac{Zr}{n a_\mu}\right) L_{n+l}^{2l+1} \left(\frac{2Zr}{n a_\mu}\right),\]

where $\frac{1}{\mu} = \frac{1}{m_1}+\frac{1}{m_2}$, $a_\mu = a_0 \frac{m_\mathrm{e}}{\mu}$, $Z = - z_1 z_2$, the Laguerre polynomials are defined as $L_n(x) = \frac{1}{n!} \mathrm{e}^x \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left( \mathrm{e}^{-x} x^n \right)$, and the associated Laguerre polynomials are defined as $L_n^{k}(x) = \frac{\mathrm{d}^k}{\mathrm{d}x^k} L_n(x)$. Note that replace $2n(n+l)!$ with $2n[(n+l)!]^3$ if the Laguerre polynomials are defined as $L_n(x) = \mathrm{e}^x \frac{\mathrm{d}^n}{\mathrm{d}x ^n} \left( \mathrm{e}^{-x} x^n \right)$. Note that replace $L_{n+l}^{2l+1}(x)$ with $- L_{n-l-1}^{2l+1}(x)$ if the associated Laguerre polynomials are defined as $L_n^{k}(x) = (-1)^k \frac{\mathrm{d}^k}{\mathrm{d}x^k} L_{n+k}(x)$, which we call the generalized Laguerre polynomials. The domain is $0\leq r \lt \infty$.

spherical_harmonic(model::CoulombTwoBody, θ, φ; l=0, m=0)

\[Y_{lm}(\theta,\varphi) = (-1)^{\frac{|m|+m}{2}} \sqrt{\frac{2l+1}{4\pi} \frac{(l-|m|)!}{(l+|m|)!}} P_l^{|m|} (\cos\theta) \mathrm{e}^{im\varphi}.\]

The domain is $0\leq \theta \lt \pi, 0\leq \varphi \lt 2\pi$. Note that some variants are connected by

\[i^{|m|+m} \sqrt{\frac{(l-|m|)!}{(l+|m|)!}} P_l^{|m|} = (-1)^{\frac{|m|+m}{2}} \sqrt{\frac{(l-|m|)!}{(l+|m|)!}} P_l^{|m|} = (-1)^m \sqrt{\frac{(l-m)!}{(l+m)!}} P_l^{m}.\]

wavefunction(model::CoulombTwoBody, r, θ, φ; n::Integer=1, l::Integer=0, m::Integer=0)

\[\psi_{nlm}(\pmb{r}) = R_{nl}(r) Y_{lm}(\theta,\varphi)\]

The domain is $0\leq r \lt \infty, 0\leq \theta \lt \pi, 0\leq \varphi \lt 2\pi$.