Orbital-Corrected Orbital-Free Density Functional Theory

理论化学的梦想是从第一原理高度精确地预测凝聚相现象。目前的理论方法要么不能始终以高精度处理化学反应，要么受到系统大小或过程时间尺度的限制。固态系统的传统理论处理是标准的平面波周期密度泛函理论（DFT），但受到计算成本和精度水平的限制。为了实现更好的缩放和准确性，我们在很大程度上依赖于DFT和改进现有的DFT的实现。解决DFT问题的两种方法中的每一种，即，传统的基于轨道的Kohn-Sham（KS）和无轨道（OF）格式各有优缺点。最近，我们开发了一种新的DFT实现，即轨道校正的OF-DFT（OO-DFT），它结合了OF-DFT和KS-DFT的优点，避免了缺点，并允许在不同的化学键合环境中的系统进行研究，比传统的自洽KS-DFT方法的成本低得多。对于金刚石Si和面心立方Ag系统，OO-DFT最多只需两次非自洽迭代即可达到完全自洽KS-DFT的精度。在此资助期内，我们将进一步发展OO-DFT，使OO-DFT通过采用目前可用的线性标度KS-DFT算法实现线性标度，并成为一个强大的工具，以处理不同化学键合环境中的数千个原子的大型系统，比其他目前可用的线性标度DFT方法更有效。我们将在从头算分子动力学（AIMD）中实现OO-DFT，以便整个理论/计算化学界可以普遍使用高效准确的基于OO-DFT的AIMD方法。最后，理论技术将成熟，为科学界提供一个可靠的工具，以定性和定量地提供对复杂系统中基本机制的微观理解，并获得对自然界中无法通过实验手段轻易探测的方面的见解。

The dream of theoretical chemistry is highly accurate predictions of condensed-phase phenomena from first principles. Current theoretical methods either cannot consistently treat chemical reactions at a high level of accuracy, or are limited by system size or the time scale of the process. The conventional theoretical treatment of solid-state systems is the standard plane-wave periodic density-functional theory (DFT), but is limited by the scaling of computational cost and the level of accuracy. To achieve better scaling and accuracy, we rely heavily on DFT and improve the existing implementations of DFT. Each of the two ways of solving the DFT problem, i.e., the traditional orbital-based Kohn-Sham (KS) and the orbital-free (OF) schemes, has its own strengths and weaknesses. Recently, we have developed a new implementation of DFT, namely orbital-corrected OF-DFT (OO-DFT), which coalesces the advantages and avoids the drawbacks of OF-DFT and KS-DFT and allows systems within different chemical bonding environments to be studied at a much lower cost than the traditional self-consistent KS-DFT method. For the cubic-diamond Si and the face-centered-cubic Ag systems, OO-DFT accomplishes accuracy comparable to fully self-consistent KS-DFT with at most two non-self-consistent iterations. In this grant period, we will further develop OO-DFT, so that OO-DFT achieves linear scaling by employing currently available linear-scaling KS-DFT algorithms and becomes a powerful tool to treat large systems of thousands of atoms within different chemical bonding environments much more efficiently than other currently available linear-scaling DFT methods. We will implement OO-DFT into ab initio molecular dynamics (AIMD) so that a highly efficient and accurate OO-DFT-based AIMD method will be available for general usage by the entire theoretical/computational chemistry community. In the end, the theoretical techniques will be matured to offer the scientific community a reliable vehicle to provide qualitatively and quantitatively a microscopic understanding of basic mechanisms in complex systems, and to gain insights into aspects of nature that cannot be easily probed by experimental means.