基于完全活性空间自洽场的杂化多组态密度泛函方法λ-DFCAS

λ-DFCAS:A Hybrid Density Functional Complete Active Space Self Consistent Field Method

提出了一种杂化多组态密度泛函新方法——λ-DFCAS.在λ-DFCAS方法中,电子相关能被分为静态和动态相关能.静态相关能由多组态波函数方法完全活性空间自洽场(CASSCF)得到,而动态相关能由密度泛函理论方法描述.两种相关能的杂化比例由一个可调节的参数λ控制.参数λ的取值取决于分子体系的多组态特性,在0~1之间变化,从而使得λ-DFCAS可以应用于各种强相关分子体系.该方法能够以与CASSCF相当的计算代价获得接近完全活性空间二阶微扰(CASPT2)的计算精度,并具备了大小一致性.

A multireference density functional theory method,namedλ-DFCAS,is presented in this paper.Based on the strategy used in λ-DFVB method,the λ-DFCAS method divides electronic correlation into two parts:the static correlation is covered by multi-reference wave function method,complete active space self-consistent field(CASSCF),while the dynamic correlation is provided by Kohn-Sham density functional theory(KS-DFT).The parameter λ in λ-DFCAS,controlling the hybrid extent of dynamic and static correlations,varies according to the multireference character of a given molecular system.The λ-DFCAS method provides a multireference density functional theory with size-consistency.Test examples show that the accuracy of λ-DFCAS is close to the complete active space second perturbation theory(CASPT2)method,while its computational cost is roughly the same as CASSCF.