We visualize the Kohn-Sham kinetic energy density (KED), and the ingredients -- the electron density, its gradient and Laplacian -- used to construct orbital-free models of it, for the AE6 test set of molecules. These are compared to related quantities used in metaGGA's, to characterize two important limits -- the gradient expansion and the localized-electron limit typified by the covalent bond. We find the second-order gradient expansion of the KED to be a surprisingly successful predictor of the exact KED, particularly at low densities where this approximation fails for exchange. This contradicts the conjointness conjecture that the optimal enhancement factors for orbital-free kinetic and exchange energy functionals are identical. In addition we find significant problems with a recent metaGGA-level orbital-free KED, especially for regions of strong electron localization. We define an orbital-free description of electron localization and a revised metaGGA that improves upon atomization energies significantly.
The Kohn-Sham approach to time-dependent density-functional theory (TDDFT) can be formulated, in principle exactly, by invoking the force-balance equation for the density, which leads to an explicit expression for the exchange-correlation potential as an implicit density functional. It is shown that this suggests a reformulation of TDDFT in terms of the second time derivative of the density, rather than the density itself. The result is a time-local Kohn-Sham scheme of second order in time whose causal structure is more transparent than that of the usual Kohn-Sham formalism. The scheme can be …
We propose a new generalised Kohn-Sham or constrained hybrid method, where the exchange potential is the (equally weighted) average of the nonlocal Fock exchange term and the self-interaction-corrected exchange potential, as obtained from our constrained minimisation method of semi-local approximations. The new method gives an accurate single-particle eigenvalue spectrum with an average deviation between (the negative of) the valence orbital eigenvalues and the experimental ionisation potentials of about 0.5eV, while the deviation of core orbitals is within 2eV. The improvement in the eigenval…
Charge transfer excitations from exact and approximate ensemble Kohn-Sham theory
通过研究一个精确可解的一维分子模型的最低激发态，我们证明了Kohn-Sham系综的分量可以用来描述电荷转移。此外，我们通过使用最近制定的系综Hartree交换理论[Gould和Pittalis，Phys. Rev. Lett. 119，243001（2017）]。值得注意的是，我们的研究结果表明，三重激发准确地复制在所有情况下测试的解离曲线，即使在系统中的基态能量是穷人由于强的静态相关性。单重态激发表现出较大的偏差，从精确的结果，但仍然半定量地再现。
The exact Kohn-Sham iteration of generalized density-functional theory in finite dimensions witha Moreau-Yosida regularized universal Lieb functional and an adaptive damping step is shown toconverge to the correct ground-state density.
A numerical scheme for solving the time-evolution of wave functions under the time dependent Kohn-Sham equation has been developed. Since the effective Hamiltonian depends on the wave functions, the wave functions and the effective Hamiltonian should evolve consistently with each other. For this purpose, a self-consistent loop is required at every time-step for solving the time-evolution numerically, which is computationally expensive. However, in this paper, we develop a different approach expressing a formal solution of the TD-KS equation, and prove that it is possible to solve the TD-KS equ…
University of California, Irvine（加州大学欧文分校）；Google Research（谷歌研究院）
Kohn-Sham regularizer (KSR) is a differentiable machine learning approach to finding the exchange-correlation functional in Kohn-Sham density functional theory (DFT) that works for strongly correlated systems. Here we test KSR for weak correlation. We propose spin-adapted KSR (sKSR) with trainable local, semilocal, and nonlocal approximations found by minimizing density and total energy loss. We assess the atoms-to-molecules generalizability by training on one-dimensional (1D) H, He, Li, Be, Be$^{++}$ and testing on 1D hydrogen chains, LiH, BeH$_2$, and helium hydride complexes. The generaliza…
Individual correlations in ensemble density-functional theory: State-driven/density-driven decompositions without additional Kohn-Sham systems
Gould和Pittalis [Phys. Rev. Lett. 123，016401（2019）]最近揭示了密度驱动（DD）相关能量，该能量特定于多电子系综，必须通过近似来解释。在这封信中，我们推导出一个一般的和更简单的表达式的系综权重，系综Kohn-Sham（KS）轨道，以及它们的线性响应的变化，在系综权重。由于不需要额外的状态驱动KS系统，它的评估大大简化。我们确认DD效应的重要性，并介绍了一个直接的和有前途的路线近似。
Moreau-Yosida-based Kohn-Sham Inversion for Periodic Systems
Oslo Metropolitan University（奥斯陆城市大学）；École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院）；Ludwig-Maximilians-Universität München（慕尼黑大学）；Max Planck Institute for the Structure and Dynamics of Matter（马普物质结构动力学研究所）；University of Oslo（奥斯陆大学）
A Kohn-Sham (KS) inversion determines a KS potential and orbitals corresponding to a given electron density, a procedure that has applications in developing and evaluating functionals used in density functional theory. Despite the utility of KS inversions, application of these methods among the research community is disproportionately small. We implement the KS inversion methods of Zhao-Morrison-Parr and Wu-Yang in a framework that simplifies analysis and conversion of the resulting potential in real-space. Fully documented Python scripts integrate with PySCF, a popular electronic structure pr…
Comment on "Generalization of the Kohn-Sham system that can represent arbitrary one-electron density matrices"
Hubertus J. J. van Dam [Phys. Rev. A 93，052512，2016]声称，相互作用系统的单粒子约化密度矩阵（1 RDM）可以通过虚构的非相互作用粒子的单行列式波函数来表示。van Dam在平均场框架内引入轨道，产生类似于Hartree-Fock（HF）轨道能量的能级，因此他还声称基于Koopmans定理的传统分析在1 RDM泛函理论（1 RDMFT）中是可能的。在这篇评论中，我们证明这两种说法都是没有根据的。
KSSOLV (Kohn-Sham Solver) is a MATLAB toolbox for performing Kohn-Sham density functional theory (DFT) calculations with a plane-wave basis set. KSSOLV 2.0 preserves the design features of the original KSSOLV software to allow users and developers to easily set up a problem and perform ground-state calculations as well as to prototype and test new algorithms. Furthermore, it includes new functionalities such as new iterative diagonalization algorithms, k-point sampling for electron band structures, geometry optimization and advanced algorithms for performing DFT calculations with local, semi-l…
We analyze the inverse problem of Density Functional Theory using a regularized variational method. First, we show that given $k$ and a target density $ρ$, there exist potentials having $k^{\text{th}}$ bound mixed states which densities are arbitrarily close to $ρ$. The state can be chosen pure in dimension $d=1$ and without interactions, and we provide numerical and theoretical evidence consistently leading us to conjecture that the same pure representability result holds for $d=2$, but that the set of pure-state $v$-representable densities is not dense for $d=3$. Finally, we present an inver…
This work presents a theory to unify the two independent theoretical frameworks of Kohn-Sham (KS) density functional theory (DFT) and reduced density matrix functional theory (RDMFT). The generalization of the KS orbitals to hypercomplex number systems leads to the hypercomplex KS (HCKS) theory, which extends the search space for the density in KS-DFT to a space that is equivalent to natural spin orbitals with fractional occupations in RDMFT. Thereby, HCKS is able to capture the multi-reference nature of strong correlation by dynamically varying fractional occupations. Moreover, the potential …
