444 RWTH Publication No: 567871        2016        IGPM444.pdf
TITLE Tensor Representation Techniques for Full Configuration Interaction: A Fock Space Approach Using the Canonical Product Format
AUTHORS Karl-Heinz Böhm , Mike Espig, Alexander A. Auer
ABSTRACT In this proof-of-principle study we apply tensor decomposition techniques to the Full Configuration Interaction (FCI) wavefunction in order to reduce the exponential scaling of the number of wavefunction parameters and overall computational effort. For this purpose, the wavefunction ansatz is formulated in an occupation number vector representation that ensures antisymmetry. If the canonical product format tensor decomposition is then applied, the Hamiltonian and the wavefunction can be cast into a multilinear product form. As a consequence, the number of wavefunction parameters does not scale to the power of the number of particles (or orbitals) but depends on the rank of the approximation and linearly on the number of particles. The degree of approximation can be controlled by a single threshold for the rank reduction procedure required in the algorithm. We demon- strate that using this approximation, the FCI Hamiltonian matrix and the wavefunction parameters can be stored with N5 scaling and the FCI problem can be solved with subexponential effort. The error of the approximation that is introduced is below Millihartree for a threshold of ε = 10−4 and no convergence problems are observed solving the FCI equations iteratively in the new format. While promising conceptually, all effort of the algorithm is shifted to the required rank reduction procedure after the contraction of the Hamiltonian with the coefficient tensor. At the current state, this crucial steps scales beyond N10 .
KEYWORDS Quantum chemistry, Full configuration interaction, Energy use and applications, Robust approximation, Optimization problems, Leptons, Hilbert space, Operator theory, Occupation number, Schrodinger equations
DOI 10.1063/1.4953665
PUBLICATION Journal of Chemical Physics, 144, 244102 (2016)
CORRESPONDING AUTHOR Alexander A. Auer, Email: alexander.auer@cec.mpg.de