2026-06-29T08:09:21Zhttps://docta.ucm.es/rest/oai/request

oai:docta.ucm.es:20.500.14352/922612024-07-29T23:51:22Zcom_20.500.14352_14col_20.500.14352_15

Approximating correlation effects in multiconfigurational self-consistent field calculations of spin-spin coupling constants San Fabián, Jesús Díez, Enrique García de la Vega, José Manuel Suardíaz Delrío, Reynier 544 Multi-configurational self-consistent field Complete-active space self-consistent field Electronic correlation Full configuration interaction Spin-spin interactions Black-box Coupling constants Nuclear magnetic resonance Regression analysis Descriptive statistics Química 23 Química The multiconfigurational self-consistent field MCSCF method in their approximations restricted and complete active spaces RAS and CAS provides a theoretically accurate description of the coupling constants of a wide range of molecules. To obtain accurate results, however, very large basis sets and large configuration spaces must be used. Nuclear magnetic resonance coupling constants for the equilibrium geometry have been calculated for a series of small molecules using approximated correlation contributions. The four contributions to the coupling constants Fermi contact, spin dipolar, orbital paramagnetic, and orbital diamagnetic have been calculated at the CAS and RAS MCSCF and second-order polarization propagator approximation levels using a large basis set. An additive model that considers the effect on the coupling constants from excitation of more than two electrons and from core-electron correlation is used to estimate the coupling constants. Compared with the experimental couplings, the best calculated values, which correspond to the MCSCF results, present a mean absolute error of 3.6 Hz and a maximum absolute deviation of 13.4 Hz. A detailed analysis of the different contributions and of the effects of the additive contributions on the coupling constants is carried out Ministerio de Ciencia, Innovación y Universidades (España) Universidad Autónoma de Madrid Depto. de Química Física Fac. de Ciencias Químicas TRUE pub 2024-01-10T13:30:30Z 2024-01-10T13:30:30Z 2008 journal article VoR https://hdl.handle.net/20.500.14352/92261 0021-9606 10.1063/1.2834210 1089-7690 eng CTQ2005-04469 info:eu-repo/grantAgreement/MEC//CTQ2007-66547/ES/DESARROLLO Y EVALUACION DE ELECTROCATALIZADORES PARA USO COMO CATODOS EN CELDAS DE COMBUSTIBLE TIPO PEM/ info:eu-repo/grantAgreement/MEC//CTQ2007-63332/ES/ESTRUCTURA ELECTRONICA MOLECULAR/ J. San Fabián, E. Díez, J. M. García de la Vega, R. Suardíaz; Approximating correlation effects in multiconfigurational self-consistent field calculations of spin-spin coupling constants. J. Chem. Phys. 28 February 2008; 128 (8): 084108. https://doi.org/10.1063/1.2834210 Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/ open access application/pdf American Institute of Physics