Nonadiabatic Molecular Dynamics by Multiconfiguration Pair-Density Functional Theory

Abstract

We present the first implementation of multiconfiguration pair-density functional theory (MC-PDFT) ab initio molecular dynamics. MC-PDFT is a multireference electronic structure method that in many cases has a similar accuracy (or even better accuracy) than complete active space second order perturbation theory (CASPT2) at a significantly lower computational cost. In this work we introduced MC-PDFT analytical gradients into the SHARC molecular dynamics program for ab initio, nonadiabatic molecular dynamics simulations. We verify our implementation by examining the intersystem crossing dynamics of thioformaldehyde, and we observe excellent agreement with recent CASPT2 and experimental findings. Moreover, with MC-PDFT we could perform dynamics with an active space that was computationally too expensive for CASPT2.

Analytic First-Order Derivatives of (X)MS, XDW, and RMS Variants of the CASPT2 and RASPT2 Methods

“…NEVPT2, 49,50 MCQDPT2, 27,51 and SA-DSRG-MRPT2 29 can also be used for MECI search, while MC-PDFT has been used for studying intersystem crossings. 52 Although OpenMolcas 53,54 is the program package with the original implementation of CASPT2, its analytic gradient has not been developed for 30 years. Recently, one of the authors has succeeded in this task for the single-state version of CASPT2.…”