Choice of Optimal Shift Parameter for the Intruder State Removal Techniques in Multireference Perturbation Theory

详细信息    查看全文

• 作者：Shu-Wei Chang ; Henryk A. Witek
• 刊名：Journal of Chemical Theory and Computation
• 出版年：2012
• 出版时间：November 13, 2012
• 年：2012
• 卷：8
• 期：11
• 页码：4053-4061
• 全文大小：389K
• 年卷期：v.8,no.11(November 13, 2012)
• ISSN：1549-9626

文摘

An extensive critical evaluation of intruder state removal techniques (aka shift techniques) applicable to multireference perturbation theory (MRPT) shows that the magnitude of the shift parameter 蟽 does not influence the spectroscopic parameters of diatomics to a significant degree, provided that the shift is chosen to be sufficiently large. In such case, typical variation of spectroscopic parameters over a wide range of shift parameters is smaller than 0.005 脜 for equilibrium distances, 30 cm^鈥? for harmonic vibrational frequencies, and 0.1 eV for dissociation energies. It is found that large values of 蟽 not only remove intruder states but they also bring the MRPT energies and properties closer to experimental values. The presented analysis allows us to determine optimal values of the shift parameters to be used in conjunction with various versions of MRPT; these values are recommended to replace the ad hoc values of 蟽 suggested in MRPT manuals in calculations for diatomics. Transferability of the optimal shift parameters to larger molecular systems and to other basis sets than aug-cc-pVTZ is anticipated but remains to be formally established.