DUGi

Three-center bonding analyzed from correlated and uncorrelated third-order reduced density matrices

http://dugi.udg.edu/item/http:@@@@hdl.handle.net@@10256@@11357

Several approximations to the third-order reduced density matrices (3-RDM) are applied to compute approximate three-center electron sharing indices (3c-ESI) and average number of three particles (3-AN) for correlated and uncorrelated wave functions with different atomic partition schemes. Exact and approximated 3c-ESI are calculated for a set of molecules with three-center two-electron (3c-2e) and three-center four-electron (3c-4e) bonding. Results show that 3c-2e bonding is associated with positive values of 3c-ESI irrespective of the method of calculation, atomic partition employed, and approximation to the third-order density matrix used. Single-determinant calculations yield negative 3c-ESI values for 3c-4e bonds, whereas the exact CASSCF 3c-ESIs are positive or close to zero. Some approximations to the 3-RDM preserve the negative sign of the 3-ESI for 3c-4e bonds, however they perform poorly on the calculation of 3-AN. The adequacy of the 3-RDM approximation to calculate 3-AN is also analyzed, revealing that Valdemoro’s approximation to the 3-RDM is the best approximation while Mazziotti’s and natural-orbital based approximations yield the lowest maximum errors

The following organizations are thanked for financial support: the Spanish Ministry (MICINN, Project numbers CTQ2011-23156/BQU and CTQ2011-25086/BQU and MINECO, Europa Excelencia project CTQ2013-41236-ERC), the Generalitat de Catalunya (Projects number 2009SGR637, 2014SGR931, 2009SGR528, and Xarxa de Referencia en Quimica Tearica i Computacional), the Marie Curie Career Integration grant PCI09-GA-2011-294240 (E.M.), and the FEDER fund (European Fund for Regional Development) for the Grant UNGI08-4E-003. Support for the research of M. Sola was received through the ICREA Academia 2009 prize for excellence in research funded by the DIUE of the Generalitat de Catalunya. F.F. and M.R-M, acknowledges financial support from the Beatriu de Finds program (AGAUR) for the postdoctoral grant BP_A_00339 (F.F.) and doctoral fellowship FI-DGR2014-00003 (M.R.-M.) Excellent service by the Centre de Serveis Cientifics i Academics de Catalunya (CESCA) is gratefully acknowledged

Elsevier