The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Martin Headgordon - One of the best experts on this subject based on the ideXlab platform.
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energy decomposition analysis for excimers using absolutely localized Molecular Orbitals within time dependent density functional theory and configuration interaction with single excitations
Journal of Chemical Theory and Computation, 2018Co-Authors: Qinghui Ge, Martin HeadgordonAbstract:We present an improved energy decomposition analysis (EDA) scheme for understanding interMolecular interactions in delocalized excited states, especially in excimers. In the EDA procedure, excited states are treated with linear response theory such as configuration interaction singles (CIS) or time-dependent density functional theory (TDDFT), and absolutely localized Molecular Orbitals (ALMOs) are used to define the intermediate (frozen, excitonic coupling, and polarized) states. The interMolecular interaction energy is thereby separated into frozen, excitonic splitting, polarization, and charge transfer contributions. The excitonic splitting term describes the delocalization effect as two or more degenerate local excitations coupled with each other, which is often an important binding force in excimers. A maximum overlap state-tracking procedure is introduced to connect the initial fragment excitations to the constrained intermediate states and finally to the unconstrained delocalized states of the compl...
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energy decomposition analysis for exciplexes using absolutely localized Molecular Orbitals
Journal of Chemical Physics, 2018Co-Authors: Qinghui Ge, Martin HeadgordonAbstract:An energy decomposition analysis (EDA) scheme is developed for understanding the interMolecular interaction involving molecules in their excited states. The EDA utilizes absolutely localized Molecular Orbitals to define intermediate states and is compatible with excited state methods based on linear response theory such as configuration interaction singles and time-dependent density functional theory. The shift in excitation energy when an excited molecule interacts with the environment is decomposed into frozen, polarization, and charge transfer contributions, and the frozen term can be further separated into Pauli repulsion and electrostatics. These terms can be added to their counterparts obtained from the ground state EDA to form a decomposition of the total interaction energy. The EDA scheme is applied to study a variety of systems, including some model systems to demonstrate the correct behavior of all the proposed energy components as well as more realistic systems such as hydrogen-bonding complexes (e.g., formamide-water, pyridine/pyrimidine-water) and halide (F−, Cl−)-water clusters that involve charge-transfer-to-solvent excitations.An energy decomposition analysis (EDA) scheme is developed for understanding the interMolecular interaction involving molecules in their excited states. The EDA utilizes absolutely localized Molecular Orbitals to define intermediate states and is compatible with excited state methods based on linear response theory such as configuration interaction singles and time-dependent density functional theory. The shift in excitation energy when an excited molecule interacts with the environment is decomposed into frozen, polarization, and charge transfer contributions, and the frozen term can be further separated into Pauli repulsion and electrostatics. These terms can be added to their counterparts obtained from the ground state EDA to form a decomposition of the total interaction energy. The EDA scheme is applied to study a variety of systems, including some model systems to demonstrate the correct behavior of all the proposed energy components as well as more realistic systems such as hydrogen-bonding complexe...
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an energy decomposition analysis for second order moller plesset perturbation theory based on absolutely localized Molecular Orbitals
Journal of Chemical Physics, 2015Co-Authors: Jonathan Thirman, Martin HeadgordonAbstract:An energy decomposition analysis (EDA) of interMolecular interactions is proposed for second-order Moller-Plesset perturbation theory (MP2) based on absolutely localized Molecular Orbitals (ALMOs), as an extension to a previous ALMO-based EDA for self-consistent field methods. It decomposes the canonical MP2 binding energy by dividing the double excitations that contribute to the MP2 wave function into classes based on how the excitations involve different molecules. The MP2 contribution to the binding energy is decomposed into four components: frozen interaction, polarization, charge transfer, and dispersion. Charge transfer is defined by excitations that change the number of electrons on a molecule, dispersion by interMolecular excitations that do not transfer charge, and polarization and frozen interactions by intra-Molecular excitations. The final two are separated by evaluations of the frozen, isolated wave functions in the presence of the other molecules, with adjustments for orbital response. Unlike previous EDAs for electron correlation methods, this one includes components for the electrostatics, which is vital as adjustment to the electrostatic behavior of the system is in some cases the dominant effect of the treatment of electron correlation. The proposed EDA is then applied to a variety of different systems to demonstrate that all proposed components behave correctly. This includes systems with one molecule and an external electric perturbation to test the separation between polarization and frozen interactions and various biMolecular systems in the equilibrium range and beyond to test the rest of the EDA. We find that it performs well on these tests. We then apply the EDA to a halogen bonded system to investigate the nature of the halogen bond.
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analysis of charge transfer effects in Molecular complexes based on absolutely localized Molecular Orbitals
Journal of Chemical Physics, 2008Co-Authors: Rustam Z Khaliullin, Alexis T Bell, Martin HeadgordonAbstract:A new method based on absolutely localized Molecular Orbitals (ALMOs) is proposed to measure the degree of interMolecular electron density delocalization (charge transfer) in Molecular complexes. ALMO charge transfer analysis (CTA) enables separation of the forward and backward charge transfer components for each pair of molecules in the system. The key feature of ALMO CTA is that all charge transfer terms have corresponding well defined energetic effects that measure the contribution of the given term to the overall energetic stabilization of the system. To simplify analysis of charge transfer effects, the concept of chemically significant complementary occupied-virtual orbital pairs (COVPs) is introduced. COVPs provide a simple description of interMolecular electron transfer effects in terms of just a few localized Orbitals. ALMO CTA is applied to understand fundamental aspects of donor-acceptor interactions in borane adducts, synergic bonding in classical and nonclassical metal carbonyls, and multiple ...
Alessandro Genoni - One of the best experts on this subject based on the ideXlab platform.
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libraries of extremely localized Molecular Orbitals 1 model molecules approximation and Molecular Orbitals transferability
Journal of Chemical Theory and Computation, 2016Co-Authors: Benjamin Meyer, Benoit Guillot, Manuel F Ruizlopez, Alessandro GenoniAbstract:Despite more and more remarkable computational ab initio results are nowadays continuously obtained for large macroMolecular systems, the development of new linear-scaling techniques is still an open and stimulating field of research in theoretical chemistry. In this family of methods, an important role is occupied by those strategies based on the observation that molecules are generally constituted by recurrent functional units with well-defined intrinsic features. In this context, we propose to exploit the notion of extremely localized Molecular Orbitals (ELMOs) that, due to their strict localization on small Molecular fragments (e.g., atoms, bonds, or functional groups), are in principle transferable from one molecule to another. Accordingly, the construction of orbital libraries to almost instantaneously build up approximate wave functions and electron densities of very large systems becomes conceivable. In this work, the ELMOs transferability is further investigated in detail and, furthermore, suitab...
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libraries of extremely localized Molecular Orbitals 2 comparison with the pseudoatoms transferability
Journal of Chemical Theory and Computation, 2016Co-Authors: Benjamin Meyer, Benoit Guillot, Manuel F Ruizlopez, Christian Jelsch, Alessandro GenoniAbstract:Due to both technical and methodological difficulties, determining and analyzing charge densities of very large Molecular systems represents a serious challenge that, in the crystallographers community, has been mainly tackled by observing that the so-called pseudoatoms of the electron density multipole expansions are reliably transferable from molecule to molecule. This has led to the construction of pseudoatoms databanks that have allowed successful refinements of crystallographic structures of macromolecules, while taking into account their corresponding reconstructed electron distributions. A recent alternative/complement to the previous approach is represented by techniques based on extremely localized Molecular Orbitals (ELMOs) that, due to their strict localization on small Molecular fragments (e.g., atoms, bonds, and functional groups), are also in principle exportable from system to system. The ELMOs transferability has been already tested in detail, and, in this work, it has been compared to the...
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x ray constrained wave functions fundamentals and effects of the Molecular Orbitals localization
Advances in Quantum Chemistry, 2016Co-Authors: Benjamin Meyer, Alessandro GenoniAbstract:Abstract The determination of wave functions from experimental data is an appealing objective that has stimulated many researchers over the years. Among the various strategies developed to accomplish this task, the X-ray constrained wave function fitting proposed by Jayatilaka is probably the most promising and it is currently used to determine experimental electron distributions in crystals. To directly introduce an easy chemical interpretation in terms of the traditional Lewis Molecular picture without resorting to a posteriori techniques, this approach has recently been extended in order to obtain Molecular Orbitals strictly localized on small Molecular fragments (e.g., atoms, bonds, or functional groups). In this chapter, after reviewing in detail both the historical development of the “experimental” wave function methods and the theoretical foundations of the X-ray constrained wave function techniques, we analyze for the first time the effect of introducing an a priori localization of Molecular Orbitals in the framework of Jayatilaka's approach. Our results mainly show that, when large and flexible basis-sets are used in the calculations, the strong initial assumption represented by the predefined localization has limited influence due to information provided by the experimental data.
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x ray constrained extremely localized Molecular Orbitals theory and critical assessment of the new technique
Journal of Chemical Theory and Computation, 2013Co-Authors: Alessandro GenoniAbstract:Following the X-ray constrained wave function approach proposed by Jayatilaka, we have devised a new technique that allows to extract Molecular Orbitals strictly localized on small Molecular fragments from sets of experimental X-ray structure factors amplitudes. Since the novel strategy enables to obtain electron distributions that have quantum mechanical features and that can be easily interpreted in terms of traditional chemical concepts, the method can be also considered as a new useful tool for the determination and the analysis of charge densities from high-resolution X-ray experiments. In this paper, we describe in detail the theory of the new technique, which, in comparison to our preliminary work, has been improved both treating the effects of isotropic secondary extinctions and introducing a new protocol to halt the fitting procedure against the experimental X-ray scattering data. The performances of the novel strategy have been studied both in function of the basis-sets flexibility and in functi...
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Molecular Orbitals strictly localized on small Molecular fragments from x ray diffraction data
Journal of Physical Chemistry Letters, 2013Co-Authors: Alessandro GenoniAbstract:Nowadays, the electron density is recognized as a fundamental property that contains most of the information concerning the electronic structure of molecules, and, therefore, its determination from high-resolution X-ray diffraction data is becoming more and more important. In this context, we propose a new strategy for the charge density analysis, strategy in which the chemical interpretability of the multipole model is combined with the quantum mechanical rigor of the wave function-based approaches. In particular, this novel technique aims at extracting Molecular Orbitals strictly localized on small Molecular fragments (e.g., atoms, bonds, or functional groups) from a set of measured structure factors amplitudes. Preliminary tests have shown that their determination is really straightforward and, given their reliable transferability, we envisage the possibility of constructing new extremely localized Molecular orbital databases as an alternative to the existing pseudoatom libraries.
Weitao Yang - One of the best experts on this subject based on the ideXlab platform.
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coupled perturbed scf approach for calculating static polarizabilities and hyperpolarizabilities with nonorthogonal localized Molecular Orbitals
Journal of Chemical Theory and Computation, 2015Co-Authors: Shaopeng Li, Weitao Yang, Linping Hu, Liang Peng, Feng Long GuAbstract:Coupled-perturbed self-consistent-field (CPSCF) approach has been broadly used for polarizabilities and hyperpolarizabilities computation. To extend this application to large systems, we have reformulated the CPSCF equations with nonorthogonal localized Molecular Orbitals (NOLMOs). NOLMOs are the most localized representation of electronic degrees of freedom. Methods based on NOLMOs are potentially ideal for investigating large systems. In atomic orbital representation, with a static external electric field added, the wave function and SCF operator of unperturbed NOLMO-SCF wave function/Orbitals are expanded to different orders of perturbations. We have derived the corresponding equations up to the third order, which are significantly different from those of a conventional CPSCF method because of the release of the orthogonal restrictions on MOs. The solution to these equations has been implemented. Several chemical systems are used to verify our method. This work represents the first step toward efficien...
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reformulating time dependent density functional theory with non orthogonal localized Molecular Orbitals
Physical Chemistry Chemical Physics, 2010Co-Authors: Weihai Fang, Weitao YangAbstract:Time-dependent density functional theory (TDDFT) has broad application in the study of electronic response, excitation and transport. To extend such application to large and complex systems, we develop a reformulation of TDDFT equations in terms of non-orthogonal localized Molecular Orbitals (NOLMOs). NOLMO is the most localized representation of electronic degrees of freedom and has been used in ground state calculations. In atomic orbital (AO) representation, the sparsity of NOLMO is transferred to the coefficient matrix of Molecular Orbitals (MOs). Its novel use in TDDFT here leads to a very simple form of time propagation equations which can be solved with linear-scaling effort. We have tested the method for several long-chain saturated and conjugated Molecular systems within the self-consistent charge density-functional tight-binding method (SCC-DFTB) and demonstrated its accuracy. This opens up pathways for TDDFT applications to large bio- and nano- systems.
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linear scaling quantum calculations using non orthogonal localized Molecular Orbitals
Journal of Physics: Condensed Matter, 2008Co-Authors: Steven K Burger, Weitao YangAbstract:An absolute energy minimum variational principle is used for carrying out linear-scaling calculations with non-orthogonal localized Orbitals. Comparing with results based on orthogonal localized Molecular Orbitals, the method is shown to give significantly more accurate results when the localized Molecular Orbitals are allowed to be non-orthogonal. This is made possible by introducing a second minimization for approximating the inverse overlap matrix. We also show how an exact line search may be used efficiently with the conjugate gradient method for minimizing the energy functional.
Qinghui Ge - One of the best experts on this subject based on the ideXlab platform.
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energy decomposition analysis for excimers using absolutely localized Molecular Orbitals within time dependent density functional theory and configuration interaction with single excitations
Journal of Chemical Theory and Computation, 2018Co-Authors: Qinghui Ge, Martin HeadgordonAbstract:We present an improved energy decomposition analysis (EDA) scheme for understanding interMolecular interactions in delocalized excited states, especially in excimers. In the EDA procedure, excited states are treated with linear response theory such as configuration interaction singles (CIS) or time-dependent density functional theory (TDDFT), and absolutely localized Molecular Orbitals (ALMOs) are used to define the intermediate (frozen, excitonic coupling, and polarized) states. The interMolecular interaction energy is thereby separated into frozen, excitonic splitting, polarization, and charge transfer contributions. The excitonic splitting term describes the delocalization effect as two or more degenerate local excitations coupled with each other, which is often an important binding force in excimers. A maximum overlap state-tracking procedure is introduced to connect the initial fragment excitations to the constrained intermediate states and finally to the unconstrained delocalized states of the compl...
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energy decomposition analysis for exciplexes using absolutely localized Molecular Orbitals
Journal of Chemical Physics, 2018Co-Authors: Qinghui Ge, Martin HeadgordonAbstract:An energy decomposition analysis (EDA) scheme is developed for understanding the interMolecular interaction involving molecules in their excited states. The EDA utilizes absolutely localized Molecular Orbitals to define intermediate states and is compatible with excited state methods based on linear response theory such as configuration interaction singles and time-dependent density functional theory. The shift in excitation energy when an excited molecule interacts with the environment is decomposed into frozen, polarization, and charge transfer contributions, and the frozen term can be further separated into Pauli repulsion and electrostatics. These terms can be added to their counterparts obtained from the ground state EDA to form a decomposition of the total interaction energy. The EDA scheme is applied to study a variety of systems, including some model systems to demonstrate the correct behavior of all the proposed energy components as well as more realistic systems such as hydrogen-bonding complexes (e.g., formamide-water, pyridine/pyrimidine-water) and halide (F−, Cl−)-water clusters that involve charge-transfer-to-solvent excitations.An energy decomposition analysis (EDA) scheme is developed for understanding the interMolecular interaction involving molecules in their excited states. The EDA utilizes absolutely localized Molecular Orbitals to define intermediate states and is compatible with excited state methods based on linear response theory such as configuration interaction singles and time-dependent density functional theory. The shift in excitation energy when an excited molecule interacts with the environment is decomposed into frozen, polarization, and charge transfer contributions, and the frozen term can be further separated into Pauli repulsion and electrostatics. These terms can be added to their counterparts obtained from the ground state EDA to form a decomposition of the total interaction energy. The EDA scheme is applied to study a variety of systems, including some model systems to demonstrate the correct behavior of all the proposed energy components as well as more realistic systems such as hydrogen-bonding complexe...
Christian Joachim - One of the best experts on this subject based on the ideXlab platform.
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direct observation of Molecular Orbitals of pentacene physisorbed on au 111 by scanning tunneling microscope
Physical Review Letters, 2009Co-Authors: Carlos Manzano, A De Sarkar, N Chandrasekhar, Christian JoachimAbstract:Differential conductance (dI/dV) images taken with a low-temperature scanning tunneling microscope enabled the first observation of the electron probability distribution of the Molecular Orbitals of a pentacene molecule directly adsorbed on a metal surface. The three highest occupied Molecular Orbitals (HOMO, HOMO-1, and HOMO-2) and the lowest unoccupied Molecular orbital are imaged. Thus dI/dV imaging without any intervening insulating layer permits the visualization of a large variety of Molecular Orbitals in the electronic cloud of a wide-gap molecule physisorbed on a metal surface.
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molecules on insulating films scanning tunneling microscopy imaging of individual Molecular Orbitals
Physical Review Letters, 2005Co-Authors: Jascha Repp, Gerhard Meyer, Sladjana Stojkovic, Andre Gourdon, Christian JoachimAbstract:Ultrathin insulating NaCl films have been employed to decouple individual pentacene molecules electronically from the metallic substrate. This allows the inherent electronic structure of the free molecule to be preserved and studied by means of low-temperature scanning-tunneling microscopy. Thereby direct images of the unperturbed Molecular Orbitals of the individual pentacene molecules are obtained. Elastic scattering quantum chemistry calculations substantiate the experimental findings.