Zimmerman Paul M, Toulouse Julien, Zhang Zhiyong, Musgrave Charles B, Umrigar C J
Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA.
J Chem Phys. 2009 Sep 28;131(12):124103. doi: 10.1063/1.3220671.
The ground and lowest three adiabatic excited states of methylene are computed using the variational Monte Carlo and diffusion Monte Carlo (DMC) methods using progressively larger Jastrow-Slater multideterminant complete active space (CAS) wave functions. The highest of these states has the same symmetry, (1)A(1), as the first excited state. The DMC excitation energies obtained using any of the CAS wave functions are in excellent agreement with experiment, but single-determinant wave functions do not yield accurate DMC energies of the states of (1)A(1) symmetry, indicating that it is important to include in the wave function Slater determinants that describe static (strong) correlation. Excitation energies obtained using recently proposed pseudopotentials [Burkatzki et al., J. Chem. Phys. 126, 234105 (2007)] differ from the all-electron excitation energies by at most 0.04 eV.
使用变分蒙特卡罗和扩散蒙特卡罗（DMC）方法，采用逐渐增大的Jastrow - Slater多行列式完全活性空间（CAS）波函数，计算了亚甲基的基态和最低三个绝热激发态。这些态中能量最高的态与第一激发态具有相同的对称性，即((^1A_1))。使用任何一种CAS波函数得到的DMC激发能与实验结果高度吻合，但单行列式波函数无法给出((^1A_1))对称性态的准确DMC能量，这表明在波函数中包含描述静态（强）关联的斯莱特行列式非常重要。使用最近提出的赝势[Burkatzki等人，《化学物理杂志》126, 234105 (2007)]得到的激发能与全电子激发能的差异至多为0.04 eV。
