Accurate treatment of electron correlation strongly depends on the form of the electronic wavefunction in the neighborhood of the electron-electron coalescence point. Explicitly correlated method such as R12-MP2, R1-CC and QMC are specifically designed to address this problem by introducing electron-electron interparticle distance terms in the form of the wavefunction. The transcorrelated method developed by Boys and Handy used a different strategy of performing similarity transformation for treatment of the Coulomb singularity in the Hamiltonian. This talk will focus of extending the central idea of the transcorrelated method by developing the congruent transformed Hamiltonian (CTH) method. The CTH method uses an explicitly correlated wave function to perform congruent transformation of the Hamiltonian. However, unlike the similarity transformation, the congruent transformation preserves the Hermitian character of the Hamiltonian and consequently the CTH is directly amenable to standard variational methods. The CTH can be implemented in both real-space representation and in the resolution of identity (RI) representation and both representations will be presented. Practical implementation of the RI representation is inherently approximate because of the finite size of the underlying basis. The RI representation can be systematically improved by identifying certain classes of diagrams and performing summation over them. This method known as partial infinite order summation (PIOS) is analogous the diagrammatic summation in MBPT and will be presented in the context of RI-CTH method. The CTH has been applied to a series of 10 electron systems and comparison of the results with other methods will be presented. Analysis of the size-consistency of CTH method will be discussed and results for the polyhydrogen Hn system will be presented.

Resolution of identity explicitly correlated congruent transformed Hamiltonian for many-electron system

246th National Meeting (2013)

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