NAST 2.0: Magnetic Field Effects and Marcus–Levich–Jortner Theory for Complex Open-Shell Systems

Abstract

Abstract We present a new version of the nast software package for predicting the kinetics of unimolecular spin-dependent processes, including intersystem crossings, spin-forbidden reactions, and spin crossovers with nonadiabatic statistical theory. With substantial extensions and upgrades, the new nast 2.0 release enables the calculations of (1) rate constants for spin-dependent reactions in an external magnetic field, (2) Marcus–Levich–Jortner rate constants with a new mlj program for complex open-shell systems, (3) Huang–Rhys factors and reorganization energies with a new vib tool, (4) Wigner and Eckart quantum tunneling correction coefficients, (5) minimum energy crossing points with a new pymecp program interfaced with the orca electronic structure package, (6) effective Hessian with the q-chem and orca packages, (7) intrinsic reaction coordinate fits with the orca package for more advanced nast calculations with the Zhu–Nakamura transition probabilities, and (8) transition probabilities and rate constants with integration step-size control. Together, these capabilities significantly enhance the applicability of nast for studying the kinetics of spin-dependent processes even in complex open-shell systems. This paper describes the objectives and applications of the new capabilities illustrated with numerical examples. nast is an open-source software package and is available free of charge.