变分多态密度泛函理论的发展及应用

In recent years, the study of excited states becomes a hot issue for chemists. Density functional theory (DFT), as one of the most important tools in theoretical chemistry, faces lots of difficulties in computing excited states, especially for the cases with multi-reference character. In this work, we will introduce a new density functional theory approach, named as variational multistate density functional theory (vMSDFT). In this approach, the configuration coefficients as well as the Kohn-Sham orbitals can be optimized simultaneously and the static and dynamic correlations can be treated on the same footing. Thus, its accuracy is comparable to the high-level ab initio methods. This work also proposes a rigorous way to define the couplings between different configurations (or transition density functional) in vMSDFT framework. In order to avoid the double counting effect, this work will introduce a ‘point-to-point correction’ treatment to cancel the static correlation in DFT framework. Based on this theory, we will develop a new module with independent intellectual property rights, which could provide an efficient and reliable tool for the investigation of excited states. As the application, this new approach will be illustrated on the photochemical process of carotenoids and their derivatives.

激发态的研究是化学家们所关注的热点问题。然而密度泛函理论作为理论化学最重要的研究工具之一，受限于其单参考特性在计算激发态特别是涉及多参考特征的激发态时面临诸多困难。对此，本课题将发展一套普适于单参考和多参考激发态的密度泛函理论新方法“变分多态密度泛函理论”。该方法在MSDFT基础上实现了组态系数和Kohn-Sham轨道的同时优化，可以真正地实现静态和动态电子相关能的自洽计算，不但可以描述具有多参考特性的激发态，同时其精度又可与高精度多从头计算法相媲美。另一方面我们引入了一套全新的转移密度矩阵和电子相关能矫正方案用以克服静态相关能重复计算的问题。基于该理论，我们还将开发一套具有自主知识产权并能独立运行的程序模块，为激发态的研究提供一套高效可靠的理论研究工具。作为应用研究，本课题将以类胡萝卜素及其衍生物作为研究实例，实现在第一性原理下其微观反应机制的理论描述，同时也对我们程序的适用性进行标定。

本项目围绕密度泛函理论方法发展和激发态非绝热过程研究这两个理论化学领域的核心科学问题，着力于新方法的发展和新软件的开发两方面工作。具体创新性成果包括：1）提出了多参考的“变分多态密度泛函理论”(vMSDFT)，该方法结合了波函数理论和密度泛函理论的优点，可以在较小的计算代价下实现高精度的计算，还能够应用于包括锥形交叉点和电子/能量转移等过程的研究。2）建立了“直接透热态构建法”（DAC），该方法克服了传统从绝热态到透热态转换不唯一的困难，可直接获得透热/绝热势能面及透热耦合矩阵元，实现从透热表象直接研究透热/非绝热过程。基于上述方法申请人开发了具有独立知识产权的软件包（软件著作权：2021SR0236376）并在激发态及非绝热过程研究等方面取得了系列创新性成果（发表相关论文12篇）。