# MQCT: User-ready program for calculations of inelastic scattering of two molecules

## Description

A program named MQCT is developed for calculations of rotationally and vibrationally inelastic scattering of molecules using the mixed quantum/classical theory approach. Calculations of collisions between two general asymmetric top rotors are now possible, which is a feature unavailable in other existing codes. Vibrational states of diatomic molecules can also be included in the basis set expansion, to carry out calculations of ro-vibrational excitation and quenching. Minimal input for the code assumes several defaults and is very simple, easy to set-up and run by non-experts. Multiple options, available for expert calculations, are listed in the Supplemental Information. The code is parallel and takes advantage of intrinsic massive parallelism of the mixed quantum/classical approach. A Monte-Carlo sampling procedure, implemented as option in the code, enables calculations for complicated systems with many internal states and large number of partial scattering waves. The coupled-states approximation is also implemented as an option. Integral and differential cross sections can be computed for the elastic channel. Rotational symmetry of each molecule, as well as permutation symmetry of two collision partners, are implemented. Potential energy surfaces for H_2 O + He, H_2 O + H_2, and H_2 O + H_2 O are included in the code. Example input files are also provided for these systems.