N-Body:Many-Body QM:QM Vibrational Frequencies: Application to Small Hydrogen-Bonded Clusters

Author

J. Coleman Howard
Gregory S. Tschumper, Missouri University of Science and TechnologyFollow

Abstract

We present an efficient method for reproducing CCSD(T) (i.e., the coupled-cluster method with single, double and perturbative connected triple excitations) optimized geometries and harmonic vibrational frequencies for molecular clusters with the N-body:Many-body QM:QM technique. In this work, all 1-body through N-body interactions are obtained from CCSD(T) computations, and the higher-order interactions are captured at the MP2 level. The linear expressions from the many-body expansion facilitate a straightforward evaluation of geometrical derivative properties (e.g., gradients and Hessians). For (H₂O)_n clusters (n = 3-7), optimized structures obtained with the 2-body:Many-body CCSD(T):MP2 method are virtually identical to CCSD(T) optimized geometries. Harmonic vibrational frequencies calculated with this 2-body:Many-body approach differ from CCSD(T) frequencies by at most a few cm-1. These deviations can be systematically reduced by including more terms from the many-body expansion at the CCSD(T) level. Maximum deviations between CCSD(T) and 3-body:Many-body CCSD(T):MP2 frequencies are typically only a few tenths of a cm^-1 for the H₂O clusters examined in this work. These results are obtained at a fraction of the wall time of the super molecular CCSD(T) computation, and the approach is well-suited for parallelization on relatively modest computational hardware. © 2013 AIP Publishing LLC.

Recommended Citation

J. C. Howard and G. S. Tschumper, "N-Body:Many-Body QM:QM Vibrational Frequencies: Application to Small Hydrogen-Bonded Clusters," Journal of Chemical Physics, vol. 139, no. 18, article no. 184113, American Institute of Physics, Nov 2013.

The definitive version is available at https://doi.org/10.1063/1.4829463

Department(s)

Chemistry

Publication Status

Available Access

Comments

National Science Foundation, Grant 0957317

International Standard Serial Number (ISSN)

0021-9606

Document Type

Article - Journal

Document Version

Final Version

File Type

text

Language(s)

English

Rights

© 2024 American Institute of Physics, All rights reserved.

Publication Date

14 Nov 2013