title: Populations of carbonic acid isomers at 210 K from a fast two-electron reduced-density matrix theory.
abstract: Parametrization of the 2-electron reduced density matrix (2-RDM) rather than the many-electron wave function yields a new family of electronic-structure methods that are faster and more accurate than traditional coupled electron-pair methods including coupled cluster with single and double excitations. Deriving the parametrization from N-representability conditions generates a 2-RDM that captures significant correlation from triple and higher-order excitations at the cost of double excitations. We apply the parametric 2-RDM method to confirm recent experiments determining the relative thermodynamic populations of the cis-cis and cis-trans isomers of carbonic acid. In 2010 Bernard et al. showed by infrared spectroscopy that the populations of cis-cis and cis-trans isomers have a 10:1 ratio at 210 K. By use of the parametric 2-RDM method, we predict a 8:1 ratio at 210 K. Comparable ab initio methods overestimate the stability of the cis-cis isomer with 24:1 and 21:1 ratios. These 2-RDM-based methods promise to have significant applications throughout chemistry.
authors: Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
authors: Christine A
authors: CA
authors: Schwerdtfeger
authors: David A
authors: DA
authors: Mazziotti
mesh_terms: D002255:Carbonic Acid / Q000737:chemistry*; D004583:Electrons; D010084:Oxidation-Reduction; D011789:Quantum Theory; D013237:Stereoisomerism; D013696:Temperature; D013816:Thermodynamics
chemical_list: D002255:Carbonic Acid