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  1. Abstract

    While the natural transition orbital (NTO) method has allowed electronic excitations from time‐dependent Hartree‐Fock and density functional theory to be viewed in a traditional orbital picture, the extension to multicomponent molecular orbitals such as those used in relativistic two‐component methods or generalized Hartree‐Fock (GHF) or generalized Kohn‐Sham (GKS) is less straightforward due to mixing of spin‐components and the inherent inclusion of spin‐flip transitions in time‐dependent GHF/GKS. An extension of single‐component NTOs to the two‐component framework is presented, in addition to a brief discussion of the practical aspects of visualizing two‐component complex orbitals. Unlike the single‐component analog, the method explicitly describes the spin and frequently obtains solutions with several significant orbital pairs. The method is presented using calculations on a mercury atom and a CrO2Cl2complex.

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  2. Abstract

    Recent studies of the optical properties of 2D materials have reported unique phenomena and features that are absent in conventional bulk semiconductors. Many of these interesting properties, such as enhanced light‐matter coupling, gate‐tunable photoluminescence, and unusual excitonic optical selection rules arise from the nature of the two‐ and multi‐particle excited states such as strongly bound Wannier excitons and charged excitons. The theory, modeling, and ab initio calculations of these optically excited states in 2D materials are reviewed. Several analytical and ab initio approaches are introduced. These methods are compared with each other, revealing their relative strength and limitations. Recent works that apply these methods to a variety of 2D materials and material‐defect systems are then highlighted. Understanding of the optically excited states in these systems is relevant not only for fundamental scientific research of electronic excitations and correlations, but also plays an important role in the future development of quantum information science and nano‐photonics.

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  3. Abstract

    The Chronus Quantum (ChronusQ) software package is an open source (under the GNU General Public License v2) software infrastructure which targets the solution of challenging problems that arise in ab initio electronic structure theory. Special emphasis is placed on the consistent treatment of time dependence and spin in the electronic wave function, as well as the inclusion of relativistic effects in said treatments. In addition, ChronusQ provides support for the inclusion of uniform finite magnetic fields as external perturbations through the use of gauge‐including atomic orbitals. ChronusQ is a parallel electronic structure code written in modern C++ which utilizes both message passing implementation and shared memory (OpenMP) parallelism. In addition to the examination of the current state of code base itself, a discussion regarding ongoing developments and developer contributions will also be provided.

    This article is categorized under:

    Software > Quantum Chemistry

    Electronic Structure Theory > Ab Initio Electronic Structure Methods

    Electronic Structure Theory > Density Functional Theory

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  4. null (Ed.)