期刊
JOURNAL OF CHEMICAL PHYSICS
卷 130, 期 9, 页码 -出版社
AMER INST PHYSICS
DOI: 10.1063/1.3077920
关键词
carbon; configuration interactions; excited states; many-body problems; Monte Carlo methods; potential energy surfaces; wave functions
资金
- DOE [DE-FG05-08OR23340, DE-FG02-07ER46366]
- ONR [N000140510055, N000140811235]
- NSF [DMR-0535592]
We show that the recently developed phaseless auxiliary-field quantum Monte Carlo (AFQMC) method can be used to study excited states, providing an alternative to standard quantum chemistry methods. The phaseless AFQMC approach, whose computational cost scales as M-3-M-4 with system size M, has been shown to be among the most accurate many-body methods in ground state calculations. For excited states, prevention of collapse into the ground state and control of the Fermion sign/phase problem are accomplished by the approximate phaseless constraint with a trial wave function. Using the challenging C-2 molecule as a test case, we calculate the potential energy curves of the ground and two low-lying singlet excited states. The trial wave function is obtained by truncating complete active space wave functions, with no further optimization. The phaseless AFQMC results using a small basis set are in good agreement with exact full configuration-interaction calculations, while those using large basis sets are in good agreement with experimental spectroscopic constants.
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