RichMol: A general variational approach for rovibrational molecular dynamics in external electric fields

Abstract

In this paper, a general variational approach for computing the rovibrational dynamics of polyatomic molecules in the presence of external electric fields is presented. Highly accurate, full-dimensional variational calculations provide a basis of field-free rovibrational states for evaluating the rovibrational matrix elements of high-rank Cartesian tensor operators and for solving the time-dependent Schrödinger equation. The effect of the external electric field is treated as a multipole moment expansion truncated at the second hyperpolarizability interaction term. Our fully numerical and computationally efficient method has been implemented in a new program, RichMol, which can simulate the effects of multiple external fields of arbitrary strength, polarization, pulse shape, and duration. Illustrative calculations of two-color orientation and rotational excitation with an optical centrifuge of NH are discussed.

Observation of electric-quadrupole infrared transitions in water vapor

“…The electric-quadrupole moment surface was computed ab initio at the CCSD(T)/aug-cc-pVQZ level of theory in the frozen-core approximation using the CFOUR program package [27]. The quadrupole intensities and Einstein A coefficients were calculated using the generalized approach RichMol for molecular dynamics in the presence of external electric fields [28]. The basis-set convergence of the ro-vibrational line positions was carefully examined.…”

Laser-induced alignment of weakly bound molecular aggregates

“…1. We utilize a reduced-mode variational approach based on the general-molecule variational approach [33][34][35] combined with a general treatment of electric fields [36].…”

Laser-induced dynamics of molecules with strong nuclear quadrupole coupling

“…45,46 All electronic structure calculations employed the quantum chemistry package ORCA. 47,48 The quadrupole moments for the 35 Cl, 79 Br, and 127 I nuclei are Q = −81.65 mb, 313 mb, and −696 mb, respectively. 49 The calculations of the molecule-field dynamics in the basis of the nuclear-spin hyperfine states were performed in a three-step procedure: First we solved the field-free problem using the rigid-rotor Hamiltonian and obtained the rotational energies and the rotational matrix elements of the EFG and the polarizability tensors, as well as of the cos 2 θ operator, (6) and (7).…”

“…The interaction terms of higher expansion order, such as the first and second hyperpolarizability tensors, can also in principle be included into the sum in (2). 35 The time-evolution operator for the time step ∆t = t−t is computed using the split-operator method as…”