### 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*

**Abstract:**

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] http://iqmol.org/
[5] P. Jurecka, J. Sponer, J. Cerny, P. Hobza; Phys Chem Chem Phys. 8 (2006), 1985