# Source code for sympy.physics.hydrogen

from __future__ import print_function, division

from sympy import factorial, sqrt, exp, S, assoc_laguerre, Float

[docs]def R_nl(n, l, r, Z=1):
"""
Returns the Hydrogen radial wavefunction R_{nl}.

n, l
quantum numbers 'n' and 'l'
r
Z
atomic number (1 for Hydrogen, 2 for Helium, ...)

Everything is in Hartree atomic units.

Examples
========

>>> from sympy.physics.hydrogen import R_nl
>>> from sympy import var
>>> var("r Z")
(r, Z)
>>> R_nl(1, 0, r, Z)
2*sqrt(Z**3)*exp(-Z*r)
>>> R_nl(2, 0, r, Z)
sqrt(2)*(-Z*r + 2)*sqrt(Z**3)*exp(-Z*r/2)/4
>>> R_nl(2, 1, r, Z)
sqrt(6)*Z*r*sqrt(Z**3)*exp(-Z*r/2)/12

For Hydrogen atom, you can just use the default value of Z=1:

>>> R_nl(1, 0, r)
2*exp(-r)
>>> R_nl(2, 0, r)
sqrt(2)*(-r + 2)*exp(-r/2)/4
>>> R_nl(3, 0, r)
2*sqrt(3)*(2*r**2/9 - 2*r + 3)*exp(-r/3)/27

For Silver atom, you would use Z=47:

>>> R_nl(1, 0, r, Z=47)
94*sqrt(47)*exp(-47*r)
>>> R_nl(2, 0, r, Z=47)
47*sqrt(94)*(-47*r + 2)*exp(-47*r/2)/4
>>> R_nl(3, 0, r, Z=47)
94*sqrt(141)*(4418*r**2/9 - 94*r + 3)*exp(-47*r/3)/27

The normalization of the radial wavefunction is:

>>> from sympy import integrate, oo
>>> integrate(R_nl(1, 0, r)**2 * r**2, (r, 0, oo))
1
>>> integrate(R_nl(2, 0, r)**2 * r**2, (r, 0, oo))
1
>>> integrate(R_nl(2, 1, r)**2 * r**2, (r, 0, oo))
1

It holds for any atomic number:

>>> integrate(R_nl(1, 0, r, Z=2)**2 * r**2, (r, 0, oo))
1
>>> integrate(R_nl(2, 0, r, Z=3)**2 * r**2, (r, 0, oo))
1
>>> integrate(R_nl(2, 1, r, Z=4)**2 * r**2, (r, 0, oo))
1

"""
# sympify arguments
n, l, r, Z = S(n), S(l), S(r), S(Z)
n_r = n - l - 1
# rescaled "r"
a = 1/Z  # Bohr radius
r0 = 2 * r / (n * a)
# normalization coefficient
C = sqrt((S(2)/(n*a))**3 * factorial(n_r) / (2*n*factorial(n + l)))
# This is an equivalent normalization coefficient, that can be found in
# some books. Both coefficients seem to be the same fast:
# C =  S(2)/n**2 * sqrt(1/a**3 * factorial(n_r) / (factorial(n+l)))
return C * r0**l * assoc_laguerre(n_r, 2*l + 1, r0).expand() * exp(-r0/2)

[docs]def E_nl(n, Z=1):
"""
Returns the energy of the state (n, l) in Hartree atomic units.

The energy doesn't depend on "l".

Examples
========

>>> from sympy import var
>>> from sympy.physics.hydrogen import E_nl
>>> var("n Z")
(n, Z)
>>> E_nl(n, Z)
-Z**2/(2*n**2)
>>> E_nl(1)
-1/2
>>> E_nl(2)
-1/8
>>> E_nl(3)
-1/18
>>> E_nl(3, 47)
-2209/18

"""
n, Z = S(n), S(Z)
if n.is_integer and (n < 1):
raise ValueError("'n' must be positive integer")
return -Z**2/(2*n**2)

[docs]def E_nl_dirac(n, l, spin_up=True, Z=1, c=Float("137.035999037")):
"""
Returns the relativistic energy of the state (n, l, spin) in Hartree atomic
units.

The energy is calculated from the Dirac equation. The rest mass energy is
*not* included.

n, l
quantum numbers 'n' and 'l'
spin_up
True if the electron spin is up (default), otherwise down
Z
atomic number (1 for Hydrogen, 2 for Helium, ...)
c
speed of light in atomic units. Default value is 137.035999037,
taken from: http://arxiv.org/abs/1012.3627

Examples
========

>>> from sympy.physics.hydrogen import E_nl_dirac
>>> E_nl_dirac(1, 0)
-0.500006656595360

>>> E_nl_dirac(2, 0)
-0.125002080189006
>>> E_nl_dirac(2, 1)
-0.125000416028342
>>> E_nl_dirac(2, 1, False)
-0.125002080189006

>>> E_nl_dirac(3, 0)
-0.0555562951740285
>>> E_nl_dirac(3, 1)
-0.0555558020932949
>>> E_nl_dirac(3, 1, False)
-0.0555562951740285
>>> E_nl_dirac(3, 2)
-0.0555556377366884
>>> E_nl_dirac(3, 2, False)
-0.0555558020932949

"""
if not (l >= 0):
raise ValueError("'l' must be positive or zero")
if not (n > l):
raise ValueError("'n' must be greater than 'l'")
if (l == 0 and spin_up is False):
raise ValueError("Spin must be up for l==0.")
# skappa is sign*kappa, where sign contains the correct sign
if spin_up:
skappa = -l - 1
else:
skappa = -l
c = S(c)
beta = sqrt(skappa**2 - Z**2/c**2)
return c**2/sqrt(1 + Z**2/(n + skappa + beta)**2/c**2) - c**2