Understanding the many-body expansion for large systems. II. Accuracy considerations

作者：Lao Ka Un; Liu Kuan Yu; Richard Ryan M; Herbert John M

来源：Journal of Chemical Physics, 2016, 144(16): 164105.

DOI：10.1063/1.4947087

To complement our study of the role of finite precision in electronic structure calculations based on a truncated many-body expansion (MBE, or "n-body expansion"), we examine the accuracy of such methods in the present work. Accuracy may be defined either with respect to a supersystem calculation computed at the same level of theory as the n-body calculations, or alternatively with respect to high-quality benchmarks. Both metrics are considered here. In applications to a sequence of water clusters, (H2O)(N= 6-55) described at the B3LYP/cc-pVDZ level, we obtain mean absolute errors (MAEs) per H2O monomer of similar to 1.0 kcal/mol for two-body expansions, where the benchmark is a B3LYP/cc-pVDZ calculation on the entire cluster. Three-and four-body expansions exhibit MAEs of 0.5 and 0.1 kcal/mol/monomer, respectively, without resort to charge embedding. A generalized many-body expansion truncated at two-body terms [ GMBE(2)], using 3-4 H2O molecules per fragment, outperforms all of these methods and affords a MAE of similar to 0.02 kcal/mol/monomer, also without charge embedding. GMBE(2) requires significantly fewer (although somewhat larger) subsystem calculations as compared to MBE(4), reducing problems associated with floating-point roundoff errors. When compared to high-quality benchmarks, we find that error cancellation often plays a critical role in the success of MBE(n) calculations, even at the four-body level, as basis-set superposition error can compensate for higher-order polarization interactions. A many-body counterpoise correction is introduced for the GMBE, and its two-body truncation [GMBCP(2)] is found to afford good results without error cancellation. Together with a method such as omega B97X-V/aug-cc-pVTZ that can describe both covalent and non-covalent interactions, the GMBE(2)+ GMBCP(2) approach provides an accurate, stable, and tractable approach for large systems. Published by AIP Publishing.

• 出版日期2016-4-28