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

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.
Authors:
 [1] ;  [2] ;  [3] ;  [1] ;  [4]
  1. University Chemical Laboratory, Lensfield Road, Cambridge CB2 1EW (United Kingdom)
  2. Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart (Germany)
  3. Department of Physics, King’s College London, Strand, London WC2R 2LS (United Kingdom)
  4. (Germany)
Publication Date:
OSTI Identifier:
22489675
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 143; Journal Issue: 13; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ALGORITHMS; CARBON; COMPARATIVE EVALUATIONS; CONFIGURATION INTERACTION; DIMERS; EXCITED STATES; GROUND STATES; MONTE CARLO METHOD; STOCHASTIC PROCESSES