Advanced concepts in vibrational configuration interaction theory (VCI)

• Applicant: Professor Dr. Guntram Rauhut
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 404988685

• Final Report Year: 2023

Final Report Abstract

An existing program for state-specific configuration-selective vibrational configuration interaction (VCI) calculations has been extended by a couple of new and fairly successful concepts, which significantly accelerate such calculations and - at the same time - lead to stabilization of these. These concepts comprise the improved handling of (quasi)-degenerate vibrational states and their proper assignment in terms of quantum numbers, the introduction of configuration classes, a new algorithm for the very efficient calculation of the vibrational angular momentum terms (as occurring in the Watson Hamiltonian) and a series of further minor imorovements. Acceleration by one to two orders of magnitude have been observed. As all of these refinements can be used in a black-box fashion, they open the way for routine VCI calculations even for unexperienced users and allow for the calculation of larger systems than before or very complex systems, which require large large correlation spaces. Benchmark calculations have been provided for a series of non-Abelian molecules and rather sensitive (quasi)-linear molecules. The generalization of this program to arbitrary orders of an n-mode expansion of the underlying n-mode expansion of the PES has been realized for the VSCF and VCI programs, but these were found to be fairly slow for several reasons. Further work in that direction is needed to allow for meaningful calculations.

Publications

• Vibrational analysis of methyl cation—Rare gas atom complexes: CH3+—Rg (Rg = He, Ne, Ar, Kr). The Journal of Chemical Physics, 150(8).
  Meisner, Jan; Hallmen, Philipp P.; Kästner, Johannes & Rauhut, Guntram
  
• Advances in vibrational configuration interaction theory ‐ part 1: Efficient calculation of vibrational angular momentum terms. Journal of Computational Chemistry, 42(32), 2321-2333.
  Mathea, Tina & Rauhut, Guntram
  
• Advances in vibrational configuration interaction theory ‐ part 2: Fast screening of the correlation space. Journal of Computational Chemistry, 43(1), 6-18.
  Mathea, Tina; Petrenko, Taras & Rauhut, Guntram
  
• A combined computational and experimental study on the vibrational structure of ethynyl isothiocyanate, HCCNCS, a molecule with a Champagne bottle potential. Journal of Molecular Spectroscopy, 386, 111626.
  Mathea, Tina; Lu, Bo; Zeng, Xiaoqing; Schröder, Benjamin & Rauhut, Guntram
  
• Vibrational Configuration Interaction Theory. Vibrational Dynamics of Molecules, 1-40. WORLD SCIENTIFIC.
  Schröder, Benjamin & Rauhut, Guntram