Related Experiment Video
Updated: May 29, 2026

Generation and Coherent Control of Pulsed Quantum Frequency Combs
Published on: June 8, 2018
Communication: extended multi-state complete active space second-order perturbation theory: energy and nuclear
Toru Shiozaki1, Werner Gyorffy, Paolo Celani
1Institut für Theoretische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
Abstract:
The extended multireference quasi-degenerate perturbation theory, proposed by Granovsky [J. Chem. Phys. 134, 214113 (2011)], is combined with internally contracted multi-state complete active space second-order perturbation theory (XMS-CASPT2). The first-order wavefunction is expanded in terms of the union of internally contracted basis functions generated from all the reference functions, which guarantees invariance of the theory with respect to unitary rotations of the reference functions. The method yields improved potentials in the vicinity of avoided crossings and conical intersections. The theory for computing nuclear energy gradients for MS-CASPT2 and XMS-CASPT2 is also presented and the first implementation of these gradient methods is reported. A number of illustrative applications of the new methods are presented.
Related Concept Videos
Atomic Nuclei: Nuclear Relaxation Processes
State Space Representation
Consider an RLC circuit, a...
Atomic Nuclei: Nuclear Spin State Overview
Atomic Nuclei: Nuclear Spin State Population Distribution
Nuclear Overhauser Enhancement (NOE)
Energy Associated With a Charge Distribution
