Local explicit correlation methods

本项目的目的是通过引入依赖于R12的相关因子来改进局部耦合聚类方法中的基集收敛。这种方法应该适用于50-100个原子的分子，并在中等大小的基组下产生准确的结果。在第一个资助期，成功地发展了基于闭壳局部M011er-Plesset摄动理论(LMP2)的显式相关方法。这些方法现在将扩展到受限开壳LMP2和(近似)耦合团簇方法。如前所述，在相关因子(F12方法)中将使用斯莱特函数(由高斯双子的固定压缩近似)，但将扩展ANSATZ以允许使用两个或更多具有不同指数的斯莱特函数。这将提供额外的灵活性，这可能是处理核心相关性效应或较重元素所需的。所有必需的积分都将使用密度拟合近似进行计算。新方法的精确度将通过计算反应能、电离势、电子亲和能以及分子团簇的相互作用能等热力学参数来系统地研究。

The aim of the current project is to improve the basis set convergence in local coupled cluster methods by including r12-dependent correlation factors. The methods should be applicable to molecules with 50-100 atoms and yield accurate results with medium-size basis sets. In the first funding period explicitly correlated methods based on closed-shell local M011er-Plesset perturbation theory (LMP2) were successfully developed. These will now be extended to restricted open-shell LMP2 and (approximate) coupled cluster methods. As before, Slater functions (approximated by fixed contractions of Gaussian Geminals) will be used in the correlation factor (F12 methods), but the ansatz will be extended to allow for the use of two or more Slater functions with different exponents. This will provide the additional flexibility that is probably needed to treat core correlation effects or heavier elements. All required integrals will be evaluated using density fitting approximations. The accuracy the new methods will be systematically investigated by computing thermodynamic quantities such as reaction energies, ionization potentials, electron affinities, as well as interaction energies of molecular clusters.