  To avoid the combinatorial computational cost of configuration interaction
(CI), we have previously introduced the symmetric tensor decomposition CI
(STD-CI) method, where we take advantage of the antisymmetric nature of the
electronic wave function and express the CI coefficients compactly as a series
of Kronecker product states (STD series) [W. Uemura and O. Sugino, Phys. Rev.
Lett. 109, 253001 (2012)]. Here we extend the variational degrees of freedom by
using different molecular orbitals for different terms in the STD series. This
scheme is equivalent to the linear combination of the Hartree-Fock-Bogoliubov
state or the antisymmetrized geminal powers (AGP). The total energy converges
very rapidly within 0.72 $\mu$Hartree taking only 10 terms for the water
molecule, and the convergence is likewise fast for Hubbard tetramers. The
computational cost scales as the fifth power of the number of electrons and the
square of the number of terms in the STD series, indicating the promise of this
AGP-based scheme for highly accurate and efficient computation of quantum
systems.
