We present recent results from our N-body:Many-body QM:QM methodfor weakly bound clusters in which all 1-body through N-body interactions arecomputed with a high-level method, while the higher-order interactions(>N-body) are only obtained with a less demanding low-level method. Ifthe chosen low-level method accurately reproduces the >N-body effects,then the errors remain small. Implementing this scheme in the ONIOMformalism leads to linear expressions for the QM:QM energy and results instraightforward evaluation of geometrical derivative properties, includinggradients and Hessians. Here, this procedure is employed to reproduce CCSD(T)optimized structures and harmonic vibrational frequencies of (H2O)n clusters(n = 3 - 6). For all clusters, geometry optimizations performed with the2-body:Many-body CCSD(T):MP2 method yield structures which are virtuallyidentical to the CCSD(T) geometries. For vibrational frequency calculations,the 2-body:Many-body CCSD(T):MP2 frequencies typically differ from thecorresponding CCSD(T) results by, at most, a few cm-1. Maximum deviationsbetween CCSD(T) and 3-body:Many-body CCSD(T):MP2 frequencies are typicallyonly a few tenths of a cm-1. These encouraging results are obtained at a fractionof the wall time of the canonical computation.

Efficiently and accurately reproducing CCSD(T) optimized structures and vibrational frequencies of water clusters with the <i>N</i>-body: Many-body QM:QM method

245th National Meeting (2013)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.

Efficiently and accurately reproducing CCSD(T) optimized structures and vibrational frequencies of water clusters with the N-body: Many-body QM:QM method