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Embracing local suppression and enhancement of dynamic correlation effects in a CASΠDFT method for efficient description of excited states.
Faraday Discussions ( IF 3.3 ) Pub Date : 2020-06-25 , DOI: 10.1039/d0fd00050g
Katarzyna Pernal 1 , Oleg V Gritsenko
Affiliation  

The recently proposed CASΠDFT method combines the reliable description of nondynamic electron correlation with the complete active space (CAS) wavefunction and the efficient treatment of dynamic correlation by density functional theory (DFT). This marriage is accomplished by adopting the DFT correlation energy functional modified with the local correction function of the on-top pair density (Π). The role of the correction function is to sensitize the correlation functional to local effects of suppression and enhancement of dynamic correlation and to account for an adequate amount of dynamic correlation energy. In this work we show that the presence of covalent and ionic configurations in a wavefunction gives rise to spatial regions where the effects of suppression and enhancement of correlation energy, respectively, dominate. The results obtained for the potential energy curves of the excited states of the hydrogen molecule prove that CASΠDFT is reliable for states that change their character along the dissociation curve. The method is also applied to the lowest excited states of six-membered heterocyclic nitrogen compounds such as pyridine, pyrazine, pyrimidine, and pyridazine. The obtained excitation energies for the n → π* and π → π* excitations confirm the good performance of CASΠDFT for excited states. The absolute average error of the method is 0.1 eV lower than that of the CCSD method and higher by the same amount than that of the more expansive CC3 variant. Compared with the coupled cluster methods, this encouraging performance of CASΠDFT is achieved at the negligible computational cost of obtaining the correlation energy.

中文翻译:

为了有效描述激发态,在CASΠDFT方法中采用局部抑制和增强动态相关效应。

最近提出的CASΠDFT方法将非动态电子相关性的可靠描述与完整的活动空间(CAS)波函数结合在一起,并且结合了密度泛函理论(DFT)对动态相关性的有效处理。通过采用利用顶对密度(Π的局部校正函数)修改的DFT相关能量函数来完成这种婚姻)。校正功能的作用是使相关函数对抑制和增强动态相关的局部效应敏感,并考虑到足够数量的动态相关能量。在这项工作中,我们表明,在波函数中共价和离子构型的存在会引起空间区域,在空间区域中,抑制和增强相关能量的作用分别占主导。对于氢分子的激发态的势能曲线所获得的结果证明,CASΠDFT对于沿解离曲线改变其特性的状态是可靠的。该方法还适用于六元杂环氮化合物(如吡啶,吡嗪,嘧啶和哒嗪)的最低激发态。所获得的n→π*和π→π*激发的激发能证实了CASΠDFT对激发态的良好性能。该方法的绝对平均误差比CCSD方法低0.1 eV,并且比更广泛的CC3变量高出相同的数量。与耦合聚类方法相比,CASΠDFT的令人鼓舞的性能是在获得相关能量的计算成本可忽略不计的情况下实现的。
更新日期:2020-06-25
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