Multi-photon interactions

Multi-photon interactions#

Two-photon absorption#

General quadratic response functions#

A general quadratic response function

\[ \langle\langle \hat{\Omega}; \hat{V}_1, \hat{V}_2 \rangle \rangle_{\omega_1, \omega_2}^\gamma \]

can be requested, referring to the linear response of the molecular property associated with \(\hat{\Omega}\) due to the perturbation associated with \(\hat{V}_1\) and \(\hat{V}_2\) oscillating with the angular frequencies \(\omega_1\) and \(\omega_2\), respectively. The damping term \(\gamma\) is associated with the inverse lifetime of excited states.

Python script

import veloxchem as vlx

molecule = vlx.Molecule.read_xyz_string("""4
Hydrogen peroxide
O  -0.65564532 -0.06106286 -0.03621403
O   0.65564532  0.06106286 -0.03621403
H  -0.97628735  0.65082652  0.57474201
H   0.97628735 -0.65082652  0.57474201
""")

basis = vlx.MolecularBasis.read(molecule, "def2-svpd", ostream=None)

scf_drv = vlx.ScfRestrictedDriver()

scf_drv.xcfun = "b3lyp"
scf_results = scf_drv.compute(molecule, basis)

crf_drv = vlx.QuadraticResponseDriver()

crf_drv.a_operator = "electric dipole"
crf_drv.b_operator = "magnetic dipole"
crf_drv.c_operator = "electric dipole"

# available operators
#qrf.b_operator = "electric dipole"
#qrf.b_operator = "magnetic dipole"
#qrf.b_operator = "linear momentum"
#qrf.b_operator = "angular momentum"

crf_drv.a_component = "z"
crf_drv.b_component = "x"
crf_drv.c_component = "x"

crf_drv.b_frequencies = [0.0656, 0.1312]
crf_drv.c_frequencies = [0.0656, 0.1312]

crf_drv.damping = 0.004556  # 1000 cm-1

crf_results = crf_drv.compute(molecule, basis, scf_results)

General cubic response functions#

A general cubic response function

\[ \langle\langle \hat{\Omega}; \hat{V}_1, \hat{V}_2, \hat{V}_3 \rangle \rangle_{\omega_1, \omega_2, \omega_3}^\gamma \]

can be requested, referring to the linear response of the molecular property associated with \(\hat{\Omega}\) due to the perturbation associated with \(\hat{V}_1\), \(\hat{V}_2\), and \(\hat{V}_3\) oscillating with the angular frequencies \(\omega_1\), \(\omega_2\), and \(\omega_3\), respectively. The damping term \(\gamma\) is associated with the inverse lifetime of excited states.