An excited-state approach within full configuration interaction quantum Monte Carlo

N. S. Blunt; Simon D. Smart; George H. Booth; Ali Alavi

doi:10.1063/1.4932595

An excited-state approach within full configuration interaction quantum Monte Carlo

N. S. Blunt^*, Simon D. Smart, George H. Booth, Ali Alavi

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

82 Citations (Scopus)

Abstract

We present a new approach to calculate excited states with the full configuration interaction quantum Monte Carlo (FCIQMC) method. The approach uses a Gram-Schmidt procedure, instantaneously applied to the stochastically evolving distributions of walkers, to orthogonalize higher energy states against lower energy ones. It can thus be used to study several of the lowest-energy states of a system within the same symmetry. This additional step is particularly simple and computationally inexpensive, requiring only a small change to the underlying FCIQMC algorithm. No trial wave functions or partitioning of the space is needed. The approach should allow excited states to be studied for systems similar to those accessible to the ground-state method due to a comparable computational cost. As a first application, we consider the carbon dimer in basis sets up to quadruple-zeta quality and compare to existing results where available.

Original language	English
Article number	134117
Journal	Journal of Chemical Physics
Volume	143
Issue number	13
DOIs	https://doi.org/10.1063/1.4932595
Publication status	Published - 7 Oct 2015

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AB - We present a new approach to calculate excited states with the full configuration interaction quantum Monte Carlo (FCIQMC) method. The approach uses a Gram-Schmidt procedure, instantaneously applied to the stochastically evolving distributions of walkers, to orthogonalize higher energy states against lower energy ones. It can thus be used to study several of the lowest-energy states of a system within the same symmetry. This additional step is particularly simple and computationally inexpensive, requiring only a small change to the underlying FCIQMC algorithm. No trial wave functions or partitioning of the space is needed. The approach should allow excited states to be studied for systems similar to those accessible to the ground-state method due to a comparable computational cost. As a first application, we consider the carbon dimer in basis sets up to quadruple-zeta quality and compare to existing results where available.

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An excited-state approach within full configuration interaction quantum Monte Carlo

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