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) the complete active space second-order perturbation theory (CASPT2) at a significantly lower computational cost. In this study, 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 simulations with the 12 electron in 10 orbitals active space that was computationally too expensive for direct dynamics with CASPT2.

Electronic structure of strongly correlated systems: recent developments in multiconfiguration pair-density functional theory and multiconfiguration nonclassical-energy functional theory

“…MC-PDFT has also been used to calculate the SOC effect in Ce + and CeH + , and MC-PDFT and XMS-PDFT provide a spin-orbit energy closer to the experimental value than does SA-CASSCF. 138 In two recent articles, 139,140 we have used MC-PDFT to study the photodynamics of SOC-promoted intersystem crossing. A greater range of photochemical processes will soon be available to PDFT methods because our group has recently completed the coding for efficient CMS-PDFT analytic gradients, as discussed in the next section.…”

“…In two recent articles, 139,140 we have used MC-PDFT to study the photodynamics of SOC-promoted intersystem crossing. A greater range of photochemical processes will soon be available to PDFT methods because our group has recently completed the coding for efficient CMS-PDFT analytic gradients, as discussed in the next section.…”

Diabatic States of Molecules

“…The input to semiclassical dynamical simulations in the diabatic representation consistsat each time stepof the DPEM and its gradient. Because of the cuspidal ridges and singularities, the APESs and NACs are almost impossible to fit accurately, and therefore calculations in the adiabatic representation are usually done by direct dynamics, which means that the information needed at each time step is calculated by on-demand electronic structure calculations. − This is expensive, and semiclassical direct dynamics in adiabatic representation calculations are often limited to short-time simulations and/or low-level electronic structure methods and/or sparse sampling of initial conditions. In contrast, because they are smooth, DPEMs can be fit to analytic functions.…”

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

“…Nonadiabatic MD simulations can be performed as well. , GVVPT2 may also be used to explore CIs, and a formulation for derivative coupling vectors exists; however, an actual implementation has not been achieved so far. NEVPT2, , MCQDPT2, , and SA-DSRG-MRPT2 can also be used for MECI search, while MC-PDFT has been used for studying intersystem crossings …”