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The DFP-LMP2 method [1,2] implemented in the CRYSCOR code[3] allows to include the electron correlation in the calculation of the ground state properties of periodic systems at the local MP2 level. It employs the Density Fitting approach in evaluating the two-electron integrals, which considerably speeds up the calculations. The method is especially powerful when weakly bound systems are investigated. The capability of treating the dispersive interaction makes this method clearly superior with respect to DFT in studying such systems.
In this context, the method becomes an attractive tool in investigating the interaction between the molecules in molecular crystals, and between molecular adsorbates and the surface. The local correlation scheme (localized orbitals, orbital domains, etc.) makes it feasible to partition the orbital pairs into different groups: inter-adsorbate, adsorbate-slab, intra-slab, etc pairs. Such partitioning allows one to focus the correlation treatment on a particular type of the interaction (e.g. adsorbate-slab interaction). This provides a deeper insight into the mechanism of the interaction and speeds up the calculations. Moreover, such partitioning makes it feasible to consider complicated systems, not manageable by the usual MP2 scheme, such as molecules adsorbed on a metallic surface. We present results of the first applications of the DFP-LMP2 method to molecular crystals and molecular adsorption on surfaces. [1] L. Maschio, D. Usvyat, F.R. Manby, S. Casassa, C. Pisani and M. Schuetz, Phys. Rev. B, in press [2] D. Usvyat, L. Maschio, F.R. Manby, S. Casassa, M. Schuetz and C. Pisani, Phys. Rev. B, in press [3] C. Pisani, M. Busso, G. Capecchi, S. Casassa, R. Dovesi, L. Maschio, C. Zicovich-Wilson, and M. Schuetz, J. Chem. Phys. 122, 094113 (2005) |
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