Session: COMP Poster Session:

For strongly interacting many-electron systems, a full configuration interaction (FCI) calculation is necessary to obtain accurate results. However, the exponential scaling of FCI limits its application to larger systems. With improved computing facilities, a lot of alternate methods like selected CI (SCI) and DMRG (density matrix renormalization group) have been able to solve larger systems but have their own limitations. The variational space for SCI becomes intractable when the active space is larger and the amount of strong correlation increases. And DMRG is most applicable for pseudo 1D systems.
In this work, we present an alternate wavefunction representation: the tensor product state (TPS) representation. We divide the active space into smaller strongly interacting clusters and solve the exact solution within that space. The final wavefunction of the system is represented in the basis of tensor products of these cluster states. We use the selected CI method in this cluster basis to represent the final wavefunction and hence call this method tensor product selected CI (TPSCI). Schmidt decomposition based truncation is used to cut down the cluster states per cluster when the cluster size increases. The number of variational degrees of freedom required is drastically reduced compared to traditional determinant based selected CI over a range of different types of systems like bond breaking in diatomics and π-conjugated systems. In this talk, a description of the TPSCI method will be given, along with a more recent extension to excited states.

Nicholas Mayhall

Virginia Tech

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