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The CRYSCOR project is currently carried on at the Theoretical Chemistry Group in Torino, and at the Regensburg Group of Physical and Theoretical Chemistry [1]. It is aimed at exploiting the availability of high-quality Hartree-Fock solutions for non-conducting crystalline systems as provided by the CRYSTAL code [2] in order to extend to periodic systems local correlation On techniques as proposed by Pulay, Werner and co-workers, and as successfully implemented in the MOLPRO program [3]. The objective is to soon provide a public code, characterized by high flexibility, generality and ease of use, for estimating the electron correlation contribution to a number of crystalline properties, first of all ground state energy. For the time being, the code is limited to the solution of local-MP2 equations, with extension to Spin Component Scaled MP2 [4]. In this presentation the main motivations for this project, the strategy adopted, the difficulties encountered and the developments envisaged in the short and long term are outlined. A large part will be devoted to the approximate evaluation of four-index composite electron-repulsion integrals, which constitute the bottleneck of all MP2 methods. The recent adaptation and implementation of local Density-Fitting techniques to Periodic systems [5,6] has reduced calculation timing up to three orders of magnitude, without any significant loss in accuracy. Other methods for integrals approximation include the multipolar expansion and the Lennard-Jones extrapolation thechniques. Present features and capabilities of the code will be shown together with examples, and a list of up-to-date feasible systems will be presented. [1] C. Pisani, M. Busso, G. Capecchi, S. Casassa, R. Dovesi, L. Maschio, C.M. Zicovich-Wilson, M. Schütz, J. Chem. Phys. 122, 094113 (2005). [2] R. Dovesi, V.R. Saunders, C. Roetti, R. Orlando, C.M. Zicovich-Wilson, F. Pascale, B. Civalleri, K. Doll, N.M. Harrison, I.J. Bush, Ph. D'Arco, M. Llunell, CRYSTAL06 User's manual. [3] H.J. Werner, P. J. Knowles, R. Lindh, F. R. Manby and M. Schütz and others, MOLPRO 2006.1 [4] S. Grimme, J. Chem. Phys. 118, 9095 (2003) [5] L. Maschio, D. Usvyat, F. R. Manby, S. Casassa, C. Pisani and M. Schütz, Phys. Rev. B in press. [6] D. Usvyat, L. Maschio, F. R. Manby, S. Casassa, M. Schütz and C. Pisani, Phys. Rev. B in press. |
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