Hirata So, Yanai Takeshi, Harrison Robert J, Kamiya Muneaki, Fan Peng-Dong
Quantum Theory Project, Department of Chemistry, University of Florida, Gainesville, Florida 32611-8435, USA.
J Chem Phys. 2007 Jan 14;126(2):024104. doi: 10.1063/1.2423005.
An assortment of computer-generated, parallel-executable programs of ab initio electron-correlation methods has been fitted with the ability to use relativistic reference wave functions. This has been done on the basis of scalar relativistic and spin-orbit effective potentials and by allowing the computer-generated programs to handle complex-valued, spinless orbitals determined by these potentials. The electron-correlation methods that benefit from this extension are high-order coupled-cluster methods (up to quadruple excitation operators) for closed- and open-shell species, coupled-cluster methods for excited and ionized states (up to quadruples), second-order perturbation corrections to coupled-cluster methods (up to triples), high-order perturbation corrections to configuration-interaction singles, and active-space (multireference) coupled-cluster methods for the ground, excited, and ionized states (up to active-space quadruples). A subset of these methods is used jointly such that the dynamical correlation energies and scalar relativistic effects are computed by a lower-order electron-correlation method with more extensive basis sets and all-electron relativistic treatment, whereas the nondynamical correlation energies and spin-orbit effects are treated by a higher-order electron-correlation method with smaller basis sets and relativistic effective potentials. The authors demonstrate the utility and efficiency of this composite scheme in chemical simulation wherein the consideration of spin-orbit effects is essential: ionization energies of rare gases, spectroscopic constants of protonated rare gases, and photoelectron spectra of hydrogen halides.
一系列从头算电子相关方法的计算机生成的并行可执行程序已具备使用相对论参考波函数的能力。这是基于标量相对论和自旋轨道有效势，并通过让计算机生成的程序处理由这些势确定的复值、无自旋轨道来实现的。受益于这一扩展的电子相关方法包括用于闭壳层和开壳层物种的高阶耦合簇方法（高达四重激发算符）、用于激发态和电离态的耦合簇方法（高达四重）、耦合簇方法的二阶微扰校正（高达三重）、配置相互作用单重态的高阶微扰校正，以及用于基态、激发态和电离态的活性空间（多参考）耦合簇方法（高达活性空间四重）。这些方法的一个子集联合使用，使得动态相关能和标量相对论效应通过具有更广泛基组和全电子相对论处理的低阶电子相关方法计算，而非动态相关能和自旋轨道效应则通过具有较小基组和相对论有效势的高阶电子相关方法处理。作者在化学模拟中展示了这种复合方案的实用性和效率，其中自旋轨道效应的考虑至关重要：稀有气体的电离能、质子化稀有气体的光谱常数以及卤化氢的光电子能谱。
