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Abstract
In this paper we propose an improved excitation generation algorithm for the full configuration interaction quantum monte carlo (FCIQMC) method, which is particularly effective in systems described by localized orbitals. The method is an extension of the precomputed heat-bath (PCHB) strategy of Holmes et al., with more effective sampling of double excitations and a novel approach for non-uniform sampling of single excitations. We demonstrate the effectiveness of the algorithm for a chain of 30 hydrogen atoms with atom-localized orbitals, a stack of benzene molecules, an Fe-porphyrin model complex, whereby we show an overall efficiency gain by a factor of two to four, as measured by variance reduction per wall-clock time.
Supplementary materials
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Supporting Information
Description
The supporting information is made available free of charge,
containing the following items:
- geometries, starting orbitals, OpenMolcas inputs, and NECI inputs
for our application test cases, and
- the code to time different (constrained) sampling strategies
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NECI codebase
Description
This is the codebase of NECI, a state-of-the-art implementation of the Full Configuration Interaction Quantum Monte Carlo (FCIQMC) algorithm, a method based on a stochastic application of the Hamiltonian matrix on a sparse sampling of the wave function. The program utilizes a very powerful parallelization and scales efficiently to more than 24 000 central processing unit cores.
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