Analytical Gradient Theory for Resolvent-Fitted Second-Order Extended Multiconfiguration Perturbation Theory (XMCQDPT2)

We present the formulation and implementation of an analytical gradient algorithm for extended multiconfiguration quasidegenerate perturbation theory (XMCQDPT2) with resolvent-fitting approximation by Granovsky. This is powerful when optimizing molecular configurations a moderate-sized active space many electronic states. First, we powerfulness accuracy approximations compared to canonical XMCQDPT2 theory. Then, demonstrate utility current in frequency analyses, minimum energy conical intersection geometries retinal chromophore model RPSB6 evaluating nuclear gradients there are Furthermore, parallelize using OpenMP/MPI hybrid approach. Additionally, report computational cost parallel efficiency program.