报告题目(Title)：电子动力学中的新型含时轨道优化耦合簇与多组态自洽场法
报告人(Speaker)：郎海峰（东京大学）
报告时间(Time)：2025年4月25日(周五) 14:40
报告地点(Place): 在线，腾讯会议室：895-921-278
邀请人(Inviter)：李永乐 教授
主办部门：8455新葡萄场网站物理系
摘要(Abstract)：
定量模拟费米子及费米子混合体系对于理解和预测分子系统的强场与超快现象至关重要（振动希尔伯特空间与各类费米子占据数均为1的混合体系同构）。当前常用的基准方法——含时多组态自洽场（TD-MCSCF）通过将部分占据轨道设为核心轨道（所有展开组态中必须占据）并限制活性空间组态相对于参考态的激发等级，可实现多项式复杂度，但存在非广延性的缺陷。
本次报告将探讨TD-MCSCF的两种新型替代方案：含时轨道优化耦合簇（TD-ooCC）方法族与多重（multiset）TD-MCSCF方法。TD-ooCC方法族采用耦合簇型参数化描述活性空间，确保广延性。该方法使用正交轨道，收敛于含时完全活性空间自洽场（TD-CASSCF），并具有良好的数值稳定性预期。
多重TD-MCSCF方法则受基于通道轨道的含时组态相互作用单激发（TD-CIS）方法与多重含时哈特里（MCTDH）方法启发。该方法可视为TD-MCSCF与TD-CIS的过渡形式，以及多重MCTDH的费米子类比。它通过非正交轨道与多组态展开实现其优越性能：具体表现为既继承了TD-CIS的低计算成本优势，又继承了TD-MCSCF可系统收敛至数值精确解的特性。本报告中其理论形式和数值模拟结果将予以展示。
Novel time-dependent orbital-optimized coupled-cluster and multiconfiguration self-consistent field ansätze for electron dynamics.
Simulating fermion and fermion mixtures quantitatively is essential for understanding and predicting strong-field and ultrafast phenomena of molecular systems (where vibrational Hilbert spaces are isomorphic to fermion mixtures with one occupation in each kind). The commonly used benchmark method, the time-dependent multiconfiguration self-consistent-field (TD-MCSCF) can achieve a polynomial cost scaling by assigning some occupied orbitals as cores (which must be occupied in all expansion configurations) and restricting configurations in the active space by the excitation levels with respect to the reference state, with a drawback of not being size extensive.
In this talk, I will discuss two novel alternates to the TD-MCSCF: time-dependent orbital optimized coupled-cluster (TD-ooCC) methods family, and multiset TD-MCSCF. TD-ooCC family employes CC-type parameterization for active space, ensuring size extensivity. They use orthogonal orbitals, converge to the time-dependent complete-active-space self-consistent-field (CASSCF)/TD-CASSCF), and are expected to be numerically stable.
Multiset TD-MCSCF is inspired by the channel orbital-based time-dependent configuration interaction singles (TD-CIS) method and the multiset multiconfiguration time-dependent Hartree (MCTDH) method. The multiset TD-MCSCF bridges TD-MCSCF and TD-CIS, serving as a fermion analogue of the multiset MCTDH. It inherits the advantage of TDCIS (low computational cost) and TD-MCSCF (controllable accuracy enabling convergence to numerically exact results) via using nonorthogonal orbitals and the multiconfigurational expansion. In this talk I will present the outline of these theories. Numerical performance will also be demonstrated.
