论文标题
多态配对密度功能理论
Multi-State Pair-Density Functional Theory
论文作者
论文摘要
以前已成功地应用了多对配对对密度函数理论(MC-PFDT)来进行地面和激发态计算。但是,由于它不包含电子状态之间的相互作用,因此MC-PDFT计算可以在圆锥形交叉点附近的区域中对势能表面(PESS)进行非物理的双重交叉。我们最近提出了状态相互作用对密度密度理论(SI-PDFT)来治疗几乎退化的状态。尽管此方法成功,但它是不方便的,因为需要两个SCF计算和两组轨道,并且因为它使基态与激发态不平等。在这里,我们提出了两种新方法,称为“扩展 - 状态-pdft”(XMS-PDFT)和变异 - 摩尔蒂 - 状态-PDFT(VMS-PDFT),它们以平衡的方式生成了中间状态,并具有一组轨道。前者使用格拉诺夫斯基提出的中间状态进行扩展的多分化准代扰动理论(XMC-QDPT);后者通过最大化中间状态的MC-PDFT能量总和来获得中间状态。我们还提出了一个傅立叶系列扩展,以方便VMS-PDFT方法的变异优化,并为常规的配置相互作用求解器和密度 - 矩阵固定型组求解器实现此方法(FMS-PDFT)。对新方法进行了八个系统的测试,这些系统在两个至六个州中都避免了穿越。 FMS-PDFT方法对于本文中研究的所有八个测试用例都成功,除混合价案外,所有这些方法都成功。由于XMS-PDFT和VMS-PDFT都比XMS-CASPT2便宜,因此它们将允许在扰动理论无法承受的更大的系统上进行良好相关的计算。
Multiconfiguration pair-density functional theory (MC-PFDT) has previously been applied successfully to carry out ground-state and excited-state calculations. However, because it includes no interaction between electronic states, MC-PDFT calculations can give an unphysical double crossing of potential energy surfaces (PESs) in a region near a conical intersection. We have recently proposed state-interaction pair-density functional theory (SI-PDFT) to treat nearly degenerate states; although this method is successful, it is inconvenient because two SCF calculations and two sets of orbitals are required and because it puts the ground state on an unequal footing with the excited states. Here we propose two new methods, called extended-multi-state-PDFT (XMS-PDFT) and variational-multi-state-PDFT (VMS-PDFT), that generate the intermediate states in a balanced way with a single set of orbitals. The former uses the intermediate states proposed by Granovsky for extended multiconfiguration quasidegenerate perturbation theory (XMC-QDPT); the latter obtains the intermediate states by maximizing the sum of the MC-PDFT energies for the intermediate states. We also propose a Fourier series expansion to make the variational optimizations of the VMS-PDFT method convenient, and we implement this method (FMS-PDFT) both for conventional configuration-interaction solvers and for density-matrix-renormalization-group solvers. The new methods are tested for eight systems exhibiting avoided crossings among two to six states. The FMS-PDFT method is successful for all eight test cases studied in the paper, and XMS-PDFT is successful for all of them except the mixed-valence case. Since both XMS-PDFT and VMS-PDFT are less expensive than XMS-CASPT2, they will allow well-correlated calculations on much larger systems for which perturbation theory is unaffordable.