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Martin Schutz - One of the best experts on this subject based on the ideXlab platform.
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local ab initio methods for calculating optical band gaps in periodic systems i periodic density fitted local configuration interaction singles method for polymers
Journal of Chemical Physics, 2011Co-Authors: Marco Lorenz, Denis Usvyat, Martin SchutzAbstract:We present a density fitted local configuration interaction singles (CIS) method for calculating optical band gaps in 1D-periodic systems. The method is based on the Davidson diagonalization procedure, carried out in the reciprocal space. The one-Electron Part of the matrix–vector products is also evaluated in the reciprocal space, where the diagonality of the Fock matrix can be exploited. The contraction of the CIS vectors with the two Electron integrals is performed in the direct space in the basis of localized occupied (Wannier) and virtual (projected atomic) orbitals. The direct space approach allows to utilize the sparsity of the integrals due to the local representation and locality of the exciton. The density fitting approximation employed for the two Electron integrals reduces the nominal scaling with unit cell size to O(N4). Test calculations on a series of prototypical systems demonstrate that the method in its present stage can be used to calculate the excitonic band gaps of polymers with up to a few dozens of atoms in the cell. The computational cost depends on the locality of the exciton, but even relatively delocalized excitons occurring in the polybiphenyl in the parallel orientation, can be routinely treated with this method.
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local ab initio methods for calculating optical band gaps in periodic systems i periodic density fitted local configuration interaction singles method for polymers
Journal of Chemical Physics, 2011Co-Authors: Marco Lorenz, Denis Usvyat, Martin SchutzAbstract:We present a density fitted local configuration interaction singles (CIS) method for calculating optical band gaps in 1D-periodic systems. The method is based on the Davidson diagonalization procedure, carried out in the reciprocal space. The one-Electron Part of the matrix–vector products is also evaluated in the reciprocal space, where the diagonality of the Fock matrix can be exploited. The contraction of the CIS vectors with the two Electron integrals is performed in the direct space in the basis of localized occupied (Wannier) and virtual (projected atomic) orbitals. The direct space approach allows to utilize the sparsity of the integrals due to the local representation and locality of the exciton. The density fitting approximation employed for the two Electron integrals reduces the nominal scaling with unit cell size to O(N4). Test calculations on a series of prototypical systems demonstrate that the method in its present stage can be used to calculate the excitonic band gaps of polymers with up to...
Marco Lorenz - One of the best experts on this subject based on the ideXlab platform.
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local ab initio methods for calculating optical band gaps in periodic systems i periodic density fitted local configuration interaction singles method for polymers
Journal of Chemical Physics, 2011Co-Authors: Marco Lorenz, Denis Usvyat, Martin SchutzAbstract:We present a density fitted local configuration interaction singles (CIS) method for calculating optical band gaps in 1D-periodic systems. The method is based on the Davidson diagonalization procedure, carried out in the reciprocal space. The one-Electron Part of the matrix–vector products is also evaluated in the reciprocal space, where the diagonality of the Fock matrix can be exploited. The contraction of the CIS vectors with the two Electron integrals is performed in the direct space in the basis of localized occupied (Wannier) and virtual (projected atomic) orbitals. The direct space approach allows to utilize the sparsity of the integrals due to the local representation and locality of the exciton. The density fitting approximation employed for the two Electron integrals reduces the nominal scaling with unit cell size to O(N4). Test calculations on a series of prototypical systems demonstrate that the method in its present stage can be used to calculate the excitonic band gaps of polymers with up to a few dozens of atoms in the cell. The computational cost depends on the locality of the exciton, but even relatively delocalized excitons occurring in the polybiphenyl in the parallel orientation, can be routinely treated with this method.
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local ab initio methods for calculating optical band gaps in periodic systems i periodic density fitted local configuration interaction singles method for polymers
Journal of Chemical Physics, 2011Co-Authors: Marco Lorenz, Denis Usvyat, Martin SchutzAbstract:We present a density fitted local configuration interaction singles (CIS) method for calculating optical band gaps in 1D-periodic systems. The method is based on the Davidson diagonalization procedure, carried out in the reciprocal space. The one-Electron Part of the matrix–vector products is also evaluated in the reciprocal space, where the diagonality of the Fock matrix can be exploited. The contraction of the CIS vectors with the two Electron integrals is performed in the direct space in the basis of localized occupied (Wannier) and virtual (projected atomic) orbitals. The direct space approach allows to utilize the sparsity of the integrals due to the local representation and locality of the exciton. The density fitting approximation employed for the two Electron integrals reduces the nominal scaling with unit cell size to O(N4). Test calculations on a series of prototypical systems demonstrate that the method in its present stage can be used to calculate the excitonic band gaps of polymers with up to...
Denis Usvyat - One of the best experts on this subject based on the ideXlab platform.
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local ab initio methods for calculating optical band gaps in periodic systems i periodic density fitted local configuration interaction singles method for polymers
Journal of Chemical Physics, 2011Co-Authors: Marco Lorenz, Denis Usvyat, Martin SchutzAbstract:We present a density fitted local configuration interaction singles (CIS) method for calculating optical band gaps in 1D-periodic systems. The method is based on the Davidson diagonalization procedure, carried out in the reciprocal space. The one-Electron Part of the matrix–vector products is also evaluated in the reciprocal space, where the diagonality of the Fock matrix can be exploited. The contraction of the CIS vectors with the two Electron integrals is performed in the direct space in the basis of localized occupied (Wannier) and virtual (projected atomic) orbitals. The direct space approach allows to utilize the sparsity of the integrals due to the local representation and locality of the exciton. The density fitting approximation employed for the two Electron integrals reduces the nominal scaling with unit cell size to O(N4). Test calculations on a series of prototypical systems demonstrate that the method in its present stage can be used to calculate the excitonic band gaps of polymers with up to a few dozens of atoms in the cell. The computational cost depends on the locality of the exciton, but even relatively delocalized excitons occurring in the polybiphenyl in the parallel orientation, can be routinely treated with this method.
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local ab initio methods for calculating optical band gaps in periodic systems i periodic density fitted local configuration interaction singles method for polymers
Journal of Chemical Physics, 2011Co-Authors: Marco Lorenz, Denis Usvyat, Martin SchutzAbstract:We present a density fitted local configuration interaction singles (CIS) method for calculating optical band gaps in 1D-periodic systems. The method is based on the Davidson diagonalization procedure, carried out in the reciprocal space. The one-Electron Part of the matrix–vector products is also evaluated in the reciprocal space, where the diagonality of the Fock matrix can be exploited. The contraction of the CIS vectors with the two Electron integrals is performed in the direct space in the basis of localized occupied (Wannier) and virtual (projected atomic) orbitals. The direct space approach allows to utilize the sparsity of the integrals due to the local representation and locality of the exciton. The density fitting approximation employed for the two Electron integrals reduces the nominal scaling with unit cell size to O(N4). Test calculations on a series of prototypical systems demonstrate that the method in its present stage can be used to calculate the excitonic band gaps of polymers with up to...
Benjamin J Schwartz - One of the best experts on this subject based on the ideXlab platform.
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the structure of the hydrated Electron Part 2 a mixed quantum classical molecular dynamics embedded cluster density functional theory single excitation configuration interaction study
Journal of Physical Chemistry A, 2007Co-Authors: Ilya A Shkrob, William J Glover, Ross E Larsen, Benjamin J SchwartzAbstract:Adiabatic mixed quantum/classical (MQC) molecular dynamics (MD) simulations were used to generate snapshots of the hydrated Electron in liquid water at 300 K. Water cluster anions that include two complete solvation shells centered on the hydrated Electron were extracted from the MQC MD simulations and embedded in a roughly 18 A × 18 A × 18 A matrix of fractional point charges designed to represent the rest of the solvent. Density functional theory (DFT) with the Becke−Lee−Yang−Parr functional and single-excitation configuration interaction (CIS) methods were then applied to these embedded clusters. The salient feature of these hybrid DFT(CIS)/MQC MD calculations is significant transfer (∼18%) of the excess Electron's charge density into the 2p orbitals of oxygen atoms in OH groups forming the solvation cavity. We used the results of these calculations to examine the structure of the singly occupied and the lower unoccupied molecular orbitals, the density of states, the absorption spectra in the visible a...
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the structure of the hydrated Electron Part 2 a mixed quantum classical molecular dynamics embedded cluster density functional theory single excitation configuration interaction study
arXiv: Data Analysis Statistics and Probability, 2006Co-Authors: Ilya A Shkrob, William J Glover, Ross E Larsen, Benjamin J SchwartzAbstract:Adiabatic mixed quantum/classical molecular dynamics simulations were used to generate snapshots of the hydrated Electron (e-) in liquid water at 300 K. Water cluster anions that include two complete solvation shells centered on the e- were extracted from these simulations and embedded in a matrix of fractional point charges designed to represent the rest of the solvent. Density functional theory and single-excitation configuration interaction methods were then applied to these embedded clusters. The salient feature of these hybrid calculations is significant transfer (ca. 0.18) of the excess Electron's charge density into the O 2p orbitals in OH groups forming the solvation cavity. We used the results of these calculations to examine the structure of the molecular orbitals, the density of states, the absorption spectra in the visible and ultraviolet, the hyperfine coupling (hfc) tensors, and the IR and Raman spectra of the e-. The calculated hfc tensors were used to compute the EPR and ESEEM spectra for the e- that compared favorably to the experimental spectra of trapped e- in alkaline ice. The calculated vibrational spectra of the e- are consistent with the red-shifted bending and stretching frequencies observed in resonance Raman experiments. The model also accounts for the VIS and 190-nm absorption bands of the e-. Thus, our study suggests that to explain several important experimentally observed properties of the e-, many-Electron effects must be accounted for.
Tsviatko K. Popov - One of the best experts on this subject based on the ideXlab platform.
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Langmuir probe measurements of the Electron energy distribution function in magnetized gas discharge plasmas
Plasma sources science & technology, 2012Co-Authors: Milan Čerček, Jernej Kovačič, Pavlina Ivanova, Marina DIMITROVA, Miglena Dimitrova, Tomaž Gyergyek, Tsviatko K. PopovAbstract:In this work, methods for using Langmuir probes (LPs) in magnetized plasmas are presented. The Electron Part of the currentvoltage probe characteristics is used to obtain the plasma potential, the Electron energy distribution function (EEDF), the Electron temperature and the Electron density. The application of LPs to EEDF evaluation in the presence of magnetic fields in the range 0.010.1T is investigated and discussed based on kinetic theory in a non-local approach. Data for EEDFs in magnetic fields in the range 0.0150.079T are acquired using currentvoltage characteristics measured in low pressure Ar and He dc gas discharges. It is also shown that the EEDFs are Maxwellian up to the energy of the first excited states of argon and helium. The values of the plasma potential, Electron temperature and density are evaluated. Comparison of the results obtained with probes perpendicular and parallel to the magnetic field results in satisfactory agreement. The results presented demonstrate that the procedures proposed allow one to acquire the main plasma parameters using the Electron Part of the currentvoltage LP characteristics in magnetized plasmas. © 2012 IOP Publishing Ltd.
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Electron energy distribution function plasma potential and Electron density measured by langmuir probe in tokamak edge plasma
Plasma Physics and Controlled Fusion, 2009Co-Authors: Tsviatko K. Popov, Pavlina Ivanova, J Stockel, R DejarnacAbstract:The Electron energy distribution function (EEDF) at different radial positions is derived from Langmuir probe measurements in the CASTOR tokamak edge plasma using the first derivative method. It is shown that the EEDFs are not Maxwellian but can be approximated as bi-Maxwellians with one dominant, low temperature Electron population and one minority composed of hotter Electrons. In the limiter shadow the measured EEDFs are Maxwellian. The values of the plasma potential and Electron densities at different radial positions are also evaluated. The results presented in this paper demonstrate that the first derivative method allows one to acquire additional plasma parameters using the Electron Part of the current–voltage characteristics in strongly magnetized tokamak edge plasmas.