第一性原理电子激发态性质计算的直接系综修正高效方法

We published on Phys. Rev. Lett. in 2017 the direct ensemble correction (DEC), a new first-principle method for calculating excited-state properties of materials. The computational cost of DEC is two orders of magnitude smaller than time-dependent density-functional theory (TDDFT), the most widely used first-principle excited-state method. Despite its very low cost, the accuracy of the DEC method is higher than TDDFT in the atomic systems we tested. For the doubly excited states which are difficult to calculate in TDDFT, the DEC method can be applied to them without the need of special treatment. Even though the DEC method has the aforementioned advantages, we only studied in our PRL the DEC method for calculating excitation energies in atoms, and further research is needed for the DEC to become a general method. In this project, we will generalize the DEC method to molecular and solid systems, further improve its accuracy, and develop DEC methods for other excited-state properties. The purpose of this project is to generalize DEC to become the method-of-choice for the calculation of excited-state properties, whose computational efficiency and accuracy are significantly better than existing first-principle methods. To demonstrate the capability of the DEC method, we will apply DEC to the study of intense laser non-sequential ionization, which lacks suitable first-principle computational method.

我们于2017年在Phys. Rev. Lett.上发表了一种新的第一性原理电子激发态性质计算方法Direct ensemble correction(DEC)，它的计算量比目前常用的TDDFT小两个数量级，但计算精度却好于TDDFT，且不需特殊处理就能对TDDFT难以计算的双电子激发态进行计算。尽管DEC有上述优势，但我们的PRL中只对原子体系的激发能计算DEC方法进行了研究，还需进行后续研究工作才能让DEC成为一种通用的方法。本项目将把DEC推广到分子和固体体系并进一步提高计算精度，研究其他激发态性质的DEC方法，最终得到一个计算效率和精度较现有第一性原理激发态性质方法有大幅提升的激发态性质计算通用方法。作为DEC方法能力的演示，我们将在强激光非时序电离问题上应用DEC方法解决这些目前缺乏合适第一性原理激发态计算研究方法的问题。

在本项目中，我们开展了材料性质第一性原理计算的方法学研究，发展了相比现有方法在精确度、计算复杂度、应用范围等方面更具优势的新方法，为材料的原子级计算仿真提供了更好的工具。我们扩展了我们之前发表的材料激发态性质计算的直接系综修正方法，推导得到了二阶微扰系综关联能近似泛函，提高了双电子激发和电荷转移激发态等在主流的含时密度泛函理论(TDDFT)中难以处理的激发态的计算精确度，且计算复杂度仍然优于线性响应TDDFT。我们为较大尺寸体系的精确高效计算提出了一种自适应第一性原理/分子力学耦合方法(QM/MM) mod-SISPA，能够根据给定活性位点自动进行区域分划而不需手动指定，并能解决现有自适应QM/MM方法难以处理共价键体系的问题。我们为自适应QM/MM方法提出了AC-AP/SDAC-AP自适应区域分划算法，能够自动根据用户指定的判据找到体系中的活性位点并进行相应区域分划，从而解决了现有所有QM/MM方法难以处理活性位点在仿真计算过程中产生/消失/变化的问题，且与大部分现有自适应QM/MM方法兼容，大幅扩展了方法的应用范围。我们为这些方法自行开发了计算仿真软件并获得了软件著作权，并针对硅材料辐射位移损伤过程进行了应用研究。

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