title: Communication: automatic code generation enables nuclear gradient computations for fully internally contracted multireference theory.
abstract: Analytical nuclear gradients for fully internally contracted complete active space second-order perturbation theory (CASPT2) are reported. This implementation has been realized by an automated code generator that can handle spin-free formulas for the CASPT2 energy and its derivatives with respect to variations of molecular orbitals and reference coefficients. The underlying complete active space self-consistent field and the so-called Z-vector equations are solved using density fitting. The implementation has been applied to the vertical and adiabatic ionization potentials of the porphin molecule to illustrate its capability.
authors: Department of Chemistry, Northwestern University, 2145 Sheridan Rd., Evanston, Illinois 60208, USA.
authors: Matthew K
authors: MK
authors: MacLeod
authors: Department of Chemistry, Northwestern University, 2145 Sheridan Rd., Evanston, Illinois 60208, USA.
authors: Toru
authors: T
authors: Shiozaki