Smith James E T, Lee Joonho, Sharma Sandeep
Center for Computational Quantum Physics, Flatiron Institute, New York, New York 10010, USA.
Department of Chemistry, Columbia University, New York, New York 10027, USA.
J Chem Phys. 2022 Sep 7;157(9):094104. doi: 10.1063/5.0085515.
In this paper, we study the nuclear gradients of heat bath configuration interaction self-consistent field (HCISCF) wave functions and use them to optimize molecular geometries for various molecules. We show that HCISCF nuclear gradients are fairly insensitive to the size of the "selected" variational space, which allows us to reduce the computational cost without introducing significant errors. The ability of the HCISCF to treat larger active spaces combined with the flexibility for users to control the computational cost makes the method very attractive for studying strongly correlated systems, which require a larger active space than possible with a complete active space self-consistent field. Finally, we study the realistic catalyst, Fe(PDI), and highlight some of the challenges this system poses for density functional theory (DFT). We demonstrate how HCISCF can clarify the energetic stability of geometries obtained from DFT when the results are strongly dependent on the functional. We also use the HCISCF gradients to optimize geometries for this species and study the adiabatic singlet-triplet gap. During geometry optimization, we find that multiple near-degenerate local minima exist on the triplet potential energy surface.
在本文中，我们研究了热浴组态相互作用自洽场（HCISCF）波函数的核梯度，并利用它们来优化各种分子的几何结构。我们表明，HCISCF核梯度对“选定”变分空间的大小相当不敏感，这使我们能够在不引入显著误差的情况下降低计算成本。HCISCF处理更大活性空间的能力，以及用户控制计算成本的灵活性，使得该方法对于研究强关联系统非常有吸引力，因为强关联系统需要比完全活性空间自洽场更大的活性空间。最后，我们研究了实际的催化剂Fe(PDI)，并强调了该系统给密度泛函理论（DFT）带来的一些挑战。我们展示了在结果强烈依赖于泛函时，HCISCF如何能够阐明从DFT获得的几何结构的能量稳定性。我们还使用HCISCF梯度来优化该物种的几何结构，并研究绝热单重态-三重态能隙。在几何结构优化过程中，我们发现在三重态势能面上存在多个近简并的局部极小值。
