Development of dynamic electron correlation model for the geminal ansatz.

V. A. Rassolov

Department of Chemistry and Biochemistry, University of South Carolina Columbia, SC 29208 USA


The geminal models of the electronic structure of molecular systems have long been considered as viable alternatives to the traditional methods based on Slater determinants [1]. In particular, the chemical systems for which a single determinant does not provide a qualitatively correct representation, known as multi-reference systems, may be amenable to the geminal description [2]. In particular, it was shown over a decade ago that a single product of strongly orthogonal geminals captures the most, if not all, multi-reference character of many challenging systems [3]. However, the important dynamic correlation effects need to be properly included into a model, to make strongly orthogonal geminals into a practical alternative to the established Density Functional Theory models. We present the development of the physics-based model of the dynamic electron correlation suitable for the strongly orthogonal geminals. It treats individual geminals as physical two-electron objects, and is (relatively) insensitive to the mathematical structure of the geminals. The development of such a model demanded a convenient tool for the analysis of the geminal wave functions, and we present the geminal visualization method as implemented in IQmol [4]. The model is applied to the traditional chemical problems of bond-breaking and of inter-molecular interactions. Latter effort is based on the S22 set of molecules [5]. [1] P. R. Surjan, in Topics in Current Chemistry ~Springer-Verlag, Berlin, 203 (1999) 63. [2] V. A. Rassolov, J. Chem. Phys. 117, (2002), 5978 [3] V.A. Rassolov, F. Xu, S. Garashchuk, J. Chem. Phys. 120 (2004) 10385 [4] [5] P. Jurecka, J. Sponer, J. Cerny, P. Hobza; Phys Chem Chem Phys. 8 (2006), 1985