Recent developments of ab initio methodology based on the correlation energy extrapolation by intrinsic scaling � full configuration interaction (CEEIS-FCI) approach [1] have been successful in yielding [2-4] the complete rotational-vibrational spectrum of near-spectroscopic accuracy for the diatomic molecules F2, O2 and B2. Our further efforts in establishing an efficient ab initio methodology have focused on the use of the seniority number [5] concept in an attempt to reduce a computational cost [6] without a significant reduction of the accuracy in computed potential energy surfaces. As a result, an efficient ab initio method has been developed and implemented [7] which uses the seniority number concept in the energy renormalization group (RG) procedure [8]. The Hamiltonian matrix (n�n) is of a very small size (n<<N, where N is the FCI-dimension) and yields the lowest n-roots representing the ground and lowest excited states. The application of this method to the symmetric dissociation of N2 and H2O molecules as well as to the symmetric dissociation of an H8 hydrogen chain demonstrates that FCI-quality potential energy curves can be obtained for ground and excited states in the systems mentioned above. New applications [9,10] of the CEEIS-FCI method to the transition metal dimers (Mo2 and Cr2) will also be discussed.References:[1] L. Bytautas, K. Ruedenberg, J. Chem. Phys. 121 , 10905 (2004).[2] L. Bytautas, N. Matsunaga, T. Nagata, M. S. Gordon, K. Ruedenberg,J. Chem. Phys. 127 , 204313 (2007).[3] L. Bytautas, N. Matsunaga, K. Ruedenberg, J. Chem. Phys. 132 , 074307 (2010).[4] L. Bytautas, N. Matsunaga, G. E. Scuseria, K. Ruedenberg,J. Phys. Chem. A 116 , 1717 (2012).[5] L. Bytautas, T. M. Henderson, C. A. Jim�nez-Hoyos, J. Ellis and G. E. Scuseria,J. Chem. Phys. 135 , 044119 (2011).[6] L. Bytautas, G. E. Scuseria, J. Dukelsky (unpublished).[7] L. Bytautas (unpublished).[8] K. G. Wilson, Rev. Mod. Phys. 47 , 773 (1975).[9] L. Bytautas, C. A. Jim�nez-Hoyos, R. Rodr�guez-Guzm�n and G. E. Scuseria,Mol. Phys. p.1-9 (2014) [online pub: January 21, 2014].[10] L. Bytautas (unpublished).

Novel developments in efficient ab initio quantum chemistry methodology

248th National Meeting (2014)

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