Using the discontinuity of the chemical potential as a function of excess charge, the fundamental... more Using the discontinuity of the chemical potential as a function of excess charge, the fundamental gaps for finite systems and the band gaps of extended solids are determined within reduced density matrix functional theory. We also present the necessary and sufficient conditions for the one-body reduced density matrix of a system with fractional charge to be ensemble N-representable. The performance of most modern day reduced density matrix functionals is assessed for the gaps and the correlation energy of finite systems. Our results show that for finite systems the PNOF, BBC3, and power functionals yield very accurate correlation energies while for a correct description of the fundamental gap the removal of self-interaction terms is essential. For extended solids we find that the power functional captures the correct band gap behavior for conventional semiconductors as well as strongly correlated Mott insulators, where a gap is obtained in absence of any magnetic ordering.
Laser pulses induce spin-selective charge flow that we show to generate dramatic changes in the m... more Laser pulses induce spin-selective charge flow that we show to generate dramatic changes in the magnetic structure of materials, including a switching of magnetic order from antiferromagnetic (AFM) to transient ferromagnetic (FM) in multisub-lattice systems. The microscopic mechanism underpinning this ultrafast switching of magnetic order is dominated by spin-selective charge transfer from one magnetic sublattice to another. Because this spin modulation is purely optical in nature (i.e., not mediated indirectly via the spin-orbit interaction) this is one of the fastest means of manipulating spin by light. We further demonstrate this mechanism to be universally applicable to AFM, FM, and ferri-magnets in both multilayer and bulk geometry and provide three rules that encapsulate early-time magnetization dynamics of multisub-lattice systems.
Proceedings of the National Academy of Sciences of the United States of America, Mar 14, 2017
The fundamental energy gap of a periodic solid distinguishes insulators from metals and character... more The fundamental energy gap of a periodic solid distinguishes insulators from metals and characterizes low-energy single-electron excitations. However, the gap in the band structure of the exact multiplicative Kohn-Sham (KS) potential substantially underestimates the fundamental gap, a major limitation of KS density-functional theory. Here, we give a simple proof of a theorem: In generalized KS theory (GKS), the band gap of an extended system equals the fundamental gap for the approximate functional if the GKS potential operator is continuous and the density change is delocalized when an electron or hole is added. Our theorem explains how GKS band gaps from metageneralized gradient approximations (meta-GGAs) and hybrid functionals can be more realistic than those from GGAs or even from the exact KS potential. The theorem also follows from earlier work. The band edges in the GKS one-electron spectrum are also related to measurable energies. A linear chain of hydrogen molecules, solid ...
Advanced materials (Deerfield Beach, Fla.), Jan 16, 2017
A conducting 2D electron gas (2DEG) is formed at the interface between epitaxial LaFeO3 layers &g... more A conducting 2D electron gas (2DEG) is formed at the interface between epitaxial LaFeO3 layers >3 unit cells thick and the surface of SrTiO3 single crystals. The 2DEG is exquisitely sensitive to cation intermixing and oxygen nonstoichiometry. It is shown that the latter thus allows the controllable formation of the 2DEG via ionic liquid gating, thereby forming a nonvolatile switch.
The electronic structure of several large gap insulators is calculated using the exact-exchange f... more The electronic structure of several large gap insulators is calculated using the exact-exchange functional (EXX) in density functional theory, and the results are compared with those from the local-density approximation (LDA) and experiment. EXX is considered a major step beyond LDA and has already been shown to provide exceptionally accurate results for semi-conductors. In this study, two classes of large
Understanding and predicting superconducting properties of real materials is of both fundamental ... more Understanding and predicting superconducting properties of real materials is of both fundamental and technological importance. In conventional systems, supercon- ductivity results from the interaction between electrons and phonons, the quantized lattice vibrations of a crystalline solid. While this basic mechanism is well under- stood within the microscopic theory of Bardeen, Cooper and Schrieer (BCS) (1) present-day theoretical methods cannot provide
A density-functional formalism comparable to the theory of Hohenberg, Kohn and Sham is developed ... more A density-functional formalism comparable to the theory of Hohenberg, Kohn and Sham is developed for electronic systems subject to time-dependent external fields. The formalism leads to a set of time-dependent Kohn-Sham equations which, in addition to the external ...
The aim of this review is to give a pedagogical introduction to our recently proposed ab initio t... more The aim of this review is to give a pedagogical introduction to our recently proposed ab initio theory of quantum transport.
Using the discontinuity of the chemical potential as a function of excess charge, the fundamental... more Using the discontinuity of the chemical potential as a function of excess charge, the fundamental gaps for finite systems and the band gaps of extended solids are determined within reduced density matrix functional theory. We also present the necessary and sufficient conditions for the one-body reduced density matrix of a system with fractional charge to be ensemble N-representable. The performance of most modern day reduced density matrix functionals is assessed for the gaps and the correlation energy of finite systems. Our results show that for finite systems the PNOF, BBC3, and power functionals yield very accurate correlation energies while for a correct description of the fundamental gap the removal of self-interaction terms is essential. For extended solids we find that the power functional captures the correct band gap behavior for conventional semiconductors as well as strongly correlated Mott insulators, where a gap is obtained in absence of any magnetic ordering.
Laser pulses induce spin-selective charge flow that we show to generate dramatic changes in the m... more Laser pulses induce spin-selective charge flow that we show to generate dramatic changes in the magnetic structure of materials, including a switching of magnetic order from antiferromagnetic (AFM) to transient ferromagnetic (FM) in multisub-lattice systems. The microscopic mechanism underpinning this ultrafast switching of magnetic order is dominated by spin-selective charge transfer from one magnetic sublattice to another. Because this spin modulation is purely optical in nature (i.e., not mediated indirectly via the spin-orbit interaction) this is one of the fastest means of manipulating spin by light. We further demonstrate this mechanism to be universally applicable to AFM, FM, and ferri-magnets in both multilayer and bulk geometry and provide three rules that encapsulate early-time magnetization dynamics of multisub-lattice systems.
Proceedings of the National Academy of Sciences of the United States of America, Mar 14, 2017
The fundamental energy gap of a periodic solid distinguishes insulators from metals and character... more The fundamental energy gap of a periodic solid distinguishes insulators from metals and characterizes low-energy single-electron excitations. However, the gap in the band structure of the exact multiplicative Kohn-Sham (KS) potential substantially underestimates the fundamental gap, a major limitation of KS density-functional theory. Here, we give a simple proof of a theorem: In generalized KS theory (GKS), the band gap of an extended system equals the fundamental gap for the approximate functional if the GKS potential operator is continuous and the density change is delocalized when an electron or hole is added. Our theorem explains how GKS band gaps from metageneralized gradient approximations (meta-GGAs) and hybrid functionals can be more realistic than those from GGAs or even from the exact KS potential. The theorem also follows from earlier work. The band edges in the GKS one-electron spectrum are also related to measurable energies. A linear chain of hydrogen molecules, solid ...
Advanced materials (Deerfield Beach, Fla.), Jan 16, 2017
A conducting 2D electron gas (2DEG) is formed at the interface between epitaxial LaFeO3 layers &g... more A conducting 2D electron gas (2DEG) is formed at the interface between epitaxial LaFeO3 layers >3 unit cells thick and the surface of SrTiO3 single crystals. The 2DEG is exquisitely sensitive to cation intermixing and oxygen nonstoichiometry. It is shown that the latter thus allows the controllable formation of the 2DEG via ionic liquid gating, thereby forming a nonvolatile switch.
The electronic structure of several large gap insulators is calculated using the exact-exchange f... more The electronic structure of several large gap insulators is calculated using the exact-exchange functional (EXX) in density functional theory, and the results are compared with those from the local-density approximation (LDA) and experiment. EXX is considered a major step beyond LDA and has already been shown to provide exceptionally accurate results for semi-conductors. In this study, two classes of large
Understanding and predicting superconducting properties of real materials is of both fundamental ... more Understanding and predicting superconducting properties of real materials is of both fundamental and technological importance. In conventional systems, supercon- ductivity results from the interaction between electrons and phonons, the quantized lattice vibrations of a crystalline solid. While this basic mechanism is well under- stood within the microscopic theory of Bardeen, Cooper and Schrieer (BCS) (1) present-day theoretical methods cannot provide
A density-functional formalism comparable to the theory of Hohenberg, Kohn and Sham is developed ... more A density-functional formalism comparable to the theory of Hohenberg, Kohn and Sham is developed for electronic systems subject to time-dependent external fields. The formalism leads to a set of time-dependent Kohn-Sham equations which, in addition to the external ...
The aim of this review is to give a pedagogical introduction to our recently proposed ab initio t... more The aim of this review is to give a pedagogical introduction to our recently proposed ab initio theory of quantum transport.
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