Benchmark Structures and Harmonic Vibrational Frequencies Near the Ccsd(T) Complete Basis Set Limit for Small Water Clusters: (H2o)n = 2, 3, 4, 5, 6

Author

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

Abstract

A series of (H₂O)_n clusters ranging from the dimer to the hexamer have been characterized with the CCSD(T) and the 2-body: Many-body CCSD(T):MP2 methods near the complete basis set (CBS) limit to generate benchmark-quality optimized structures and harmonic vibrational frequencies for these important systems. Quadruple-ζ correlation-consistent basis sets that augment the O atoms with diffuse functions have been employed in the analytic computation of harmonic vibrational frequencies for the global minima of the dimer, trimer, tetramer, and pentamer as well as the ring, book, cage, and prism isomers of the hexamer. Prior calibration [J. Chem. Phys. 2013, 139, 184113 and J. Chem. Theory Comput. 2014, 10, 5426] suggests that harmonic frequencies computed with this approach will lie within a few cm-1 of the canonical CCSD(T) CBS limit. These data are used as reference values to gauge the performance of harmonic frequencies obtained with other ab initio methods (e.g., LCCSD(T) and MP2) and water potentials (e.g., TTM3-F and WHBB). This comparison reveals that it is far more challenging to converge harmonic vibrational frequencies for the bound OH stretching modes in these (H₂O)_n clusters to the CCSD(T) CBS limit than the free OH stretches, the n intermonomer HOH bending modes and even the 6n - 6 intermonomer modes. Deviations associated with the bound OH stretching harmonic frequencies increase rapidly with the size of the cluster for all methods and potentials examined, as do the corresponding frequency shifts relative to the monomer OH stretches.

Recommended Citation

J. C. Howard and G. S. Tschumper, "Benchmark Structures and Harmonic Vibrational Frequencies Near the Ccsd(T) Complete Basis Set Limit for Small Water Clusters: (H2o)n = 2, 3, 4, 5, 6," Journal of Chemical Theory and Computation, vol. 11, no. 5, pp. 2126 - 2136, American Chemical Society, May 2015.

The definitive version is available at https://doi.org/10.1021/acs.jctc.5b00225

Department(s)

Chemistry

Publication Status

Open Access

Comments

National Science Foundation, Grant CHE-0957317

International Standard Serial Number (ISSN)

1549-9626; 1549-9618

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2024 American Chemical Society, All rights reserved.

Publication Date

12 May 2015

PubMed ID

26574415