Analytic Gradients for Complete Active Space Pair-Density Functional\n Theory

Analytic gradient routines are a desirable feature for quantum mechanical\nmethods, allowing for efficient determination of equilibrium and transition\nstate structures and several other molecular properties. In this work, we\npresent analytical gradients for multiconfiguration pair-density functional\ntheory (MC-PDFT) when used with a state-specific complete active space\nself-consistent field reference wave function. Our approach constructs a\nLagrangian that is variational in all wave function parameters. We find that\nMC-PDFT locates equilibrium geometries for several small- to medium-sized\norganic molecules that are similar to those located by complete active space\nsecond-order perturbation theory but that are obtained with decreased\ncomputational cost.\n