Approaching chemical accuracy using full configuration-interaction quantum Monte Carlo: A study of ionization potentials

被引:110
作者
Booth, George H. [1 ]
Alavi, Ali [1 ]
机构
[1] Univ Cambridge, Dept Chem, Cambridge CB2 1EW, England
基金
英国工程与自然科学研究理事会;
关键词
beryllium; boron; carbon; configuration interactions; fluorine; ionisation potential; lithium; magnesium; Monte Carlo methods; neon; nitrogen; oxygen; sodium; STATE CORRELATION ENERGIES; WAVE-FUNCTIONS; ELECTRON-AFFINITIES; ATOMIC IONS; BASIS-SETS; BENCHMARK; MOLECULES; N-2;
D O I
10.1063/1.3407895
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
A new quantum Monte Carlo (QMC) method is used to calculate exact, full configuration-interaction (FCI) energies of the neutral and cationic elements from Li to Mg, in a family of commonly used basis sets. Annihilation processes between positive and negative walkers enable the exact N-electron wave function to emerge as a linear superposition of the (factorially large) space of Slater determinants, with individual determinants being stochastically sampled. As a result, extremely large spaces (exceeding 10(15) determinants) become accessible for FCI calculations. No fixed-node approximation is necessary, and the only remaining source of error is the one-electron basis set, which can be systematically reduced by enlargement of the basis set. We have investigated the family of aug-cc-pVXZ Dunning basis sets up to X=5. The resulting ionization potentials are-with one exception (Na)-consistently accurate to within chemical accuracy. The anomalous case of Na suggests that its basis set may be improvable. Extrapolation schemes are examined as a way of further improving the values obtained, and although an improvement is seen in the mean-absolute error, the results of extrapolation are not uniformly better than the largest basis set calculations reported. More generally, these results demonstrate the utility of the QMC method to provide FCI energies for realistic systems and basis sets. (c) 2010 American Institute of Physics. [doi: 10.1063/1.3407895]
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页数:7
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