The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Georg Kresse - One of the best experts on this subject based on the ideXlab platform.
-
optimized effective potentials from the Random Phase Approximation accuracy of the quasiparticle Approximation
Journal of Chemical Physics, 2021Co-Authors: Stefan Riemelmoser, Merzuk Kaltak, Georg KresseAbstract:The optimized effective potential (OEP) method presents an unambiguous way to construct the Kohn-Sham potential corresponding to a given diagrammatic Approximation for the exchange-correlation functional. The OEP from the Random-Phase Approximation (RPA) has played an important role ever since the conception of the OEP formalism. However, the solution of the OEP equation is computationally fairly expensive and has to be done in a self-consistent way. So far, large scale solid state applications have, therefore, been performed only using the quasiparticle Approximation (QPA), neglecting certain dynamical screening effects. We obtain the exact RPA-OEP for 15 semiconductors and insulators by direct solution of the linearized Sham-Schluter equation. We investigate the accuracy of the QPA on Kohn-Sham bandgaps and dielectric constants, and comment on the issue of self-consistency.
-
cubic and tetragonal perovskites from the Random Phase Approximation
Physical Review Materials, 2019Co-Authors: Fanhao Jia, Georg Kresse, Cesare Franchini, Peitao Liu, Jing Wang, Alessandro Stroppa, Wei RenAbstract:Evaluating many-body correlation effects beyond the commonly applied local or semilocal density functionals has received tremendous attention over the past few years. Using the Random Phase Approximation to describe the correlation energy combined with the exact exchange energy, we have investigated 20 cubic $AB{\mathrm{O}}_{3}$-type perovskites and three prototypical ferroelectric (tetragonal) perovskites. A quantitative analysis and comparison of the performance of various local and semilocal exchange-correlation functionals shows that the inclusion of dynamical correlation effects allows for an excellent account of the structure and energetics of complex $AB{\mathrm{O}}_{3}$-type oxides.
-
screened exchange corrections to the Random Phase Approximation from many body perturbation theory
Journal of Chemical Theory and Computation, 2019Co-Authors: Felix Hummel, Georg Kresse, Andreas Gruneis, Paul ZiescheAbstract:The Random Phase Approximation (RPA) systematically overestimates the magnitude of the correlation energy and generally underestimates cohesive energies. This originates in part from the complete lack of exchange terms that would otherwise cancel Pauli exclusion principle violating (EPV) contributions. The uncanceled EPV contributions also manifest themselves in form of an unphysical negative pair density of spin-parallel electrons close to electron-electron coalescence. We follow considerations of many-body perturbation theory to propose an exchange correction that corrects the largest set of EPV contributions, while having the lowest possible computational complexity. The proposed method exchanges adjacent particle/hole pairs in the RPA diagrams, considerably improving the pair density of spin-parallel electrons close to coalescence in the uniform electron gas (UEG). The accuracy of the correlation energy is comparable to other variants of second-order screened exchange (SOSEX) corrections although it is slightly more accurate for the spin-polarized UEG. Its computational complexity scales as [Formula: see text] or [Formula: see text] in orbital space or real space, respectively. Its memory requirement scales as [Formula: see text].
-
adsorption energies of benzene on close packed transition metal surfaces using the Random Phase Approximation
Physical Review Materials, 2017Co-Authors: Jose Garrido A Torres, Benjamin Ramberger, Herbert A Fruchtl, Renald Schaub, Georg KresseAbstract:The adsorption energy of benzene on various metal substrates is predicted using the Random Phase Approximation (RPA) for the correlation energy. Agreement with available experimental data is systematically better than 10% for both coinage and reactive metals. The results are also compared with more approximate methods, including van der Waals density functional theory (DFT), as well as dispersion-corrected DFT functionals. Although dispersion-corrected DFT can yield accurate results, for instance, on coinage metals, the adsorption energies are clearly overestimated on more reactive transition metals. Furthermore, coverage dependent adsorption energies are well described by the RPA. This shows that for the description of aromatic molecules on metal surfaces further improvements in density functionals are necessary, or more involved many-body methods such as the RPA are required.
-
adsorption energies of benzene on close packed transition metal surfaces using the Random Phase Approximation
arXiv: Chemical Physics, 2017Co-Authors: J Garrido A Torres, Benjamin Ramberger, Herbert A Fruchtl, Renald Schaub, Georg KresseAbstract:The adsorption energy of benzene on various metal substrates is predicted using the Random Phase Approximation (RPA) for the correlation energy. Agreement with available experimental data is systematically better than 10% for both coinage and reactive metals. The results are also compared with more approximate methods, including vdW-density functional theory (DFT), as well as dispersion corrected DFT functionals. Although dispersion corrected DFT can yield accurate results, for instance, on coinage metals, the adsorption energies are clearly overestimated on more reactive transition metals. Furthermore, coverage dependent adsorption energies are well described by the RPA. This shows that for the description of aromatic molecules on metal surfaces further improvements in density functionals are necessary, or more involved many body methods such as the RPA are required.
Weitao Yang - One of the best experts on this subject based on the ideXlab platform.
-
excitation energies from particle particle Random Phase Approximation with accurate optimized effective potentials
Journal of Chemical Physics, 2017Co-Authors: Ye Jin, Yang Yang, Degao Peng, Du Zhang, Weitao YangAbstract:The optimized effective potential (OEP) that gives accurate Kohn-Sham (KS) orbitals and orbital energies can be obtained from a given reference electron density. These OEP-KS orbitals and orbital energies are used here for calculating electronic excited states with the particle-particle Random Phase Approximation (pp-RPA). Our calculations allow the examination of pp-RPA excitation energies with the exact KS density functional theory (DFT). Various input densities are investigated. Specifically, the excitation energies using the OEP with the electron densities from the coupled-cluster singles and doubles method display the lowest mean absolute error from the reference data for the low-lying excited states. This study probes into the theoretical limit of the pp-RPA excitation energies with the exact KS-DFT orbitals and orbital energies. We believe that higher-order correlation contributions beyond the pp-RPA bare Coulomb kernel are needed in order to achieve even higher accuracy in excitation energy calculations.
-
accurate quasiparticle spectra from the t matrix self energy and the particle particle Random Phase Approximation
Journal of Physical Chemistry Letters, 2017Co-Authors: Du Zhang, Weitao YangAbstract:The GW self-energy, especially G0W0 based on the particle–hole Random Phase Approximation (phRPA), is widely used to study quasiparticle (QP) energies. Motivated by the desirable features of the particle–particle (pp) RPA compared to the conventional phRPA, we explore the pp counterpart of GW, that is, the T-matrix self-energy, formulated with the eigenvectors and eigenvalues of the ppRPA matrix. We demonstrate the accuracy of the T-matrix method for molecular QP energies, highlighting the importance of the pp channel for calculating QP spectra.
-
accurate atomic quantum defects from particle particle Random Phase Approximation
Molecular Physics, 2016Co-Authors: Yang Yang, Kieron Burke, Weitao YangAbstract:ABSTRACTThe accuracy of calculations of atomic Rydberg excitations cannot be judged by the usual measures, such as mean unsigned errors of many transitions. We show how to use quantum defect (QD) theory to (a) separate errors due to approximate ionisation potentials, (b) extract smooth QDs to compare with experiment, and (c) quantify those defects with a few characteristic parameters. The particle–particle Random Phase Approximation (pp-RPA) produces excellent Rydberg transitions that are an order of magnitude more accurate than those of time-dependent density functional theory with standard Approximations. We even extract reasonably accurate defects from the lithium Rydberg series, despite the reference being open-shell. Our methodology can be applied to any Rydberg series of excitations with four transitions or more to extract the underlying threshold energy and characteristic QD parameters. Our pp-RPA results set a demanding challenge for other excitation methods to match.
-
singlet triplet energy gaps for diradicals from particle particle Random Phase Approximation
Bulletin of the American Physical Society, 2016Co-Authors: Yang Yang, Degao Peng, Ernest R Davidson, Weitao YangAbstract:The particle–particle Random Phase Approximation (pp-RPA) for calculating excitation energies has been applied to diradical systems. With pp-RPA, the two nonbonding electrons are treated in a subspace configuration interaction fashion while the remaining part is described by density functional theory (DFT). The vertical or adiabatic singlet–triplet energy gaps for a variety of categories of diradicals, including diatomic diradicals, carbene-like diradicals, disjoint diradicals, four-π-electron diradicals, and benzynes are calculated. Except for some excitations in four-π-electron diradicals, where four-electron correlation may play an important role, the singlet–triplet gaps are generally well predicted by pp-RPA. With a relatively low O(r4) scaling, the pp-RPA with DFT references outperforms spin-flip configuration interaction singles. It is similar to or better than the (variational) fractional-spin method. For small diradicals such as diatomic and carbene-like ones, the error of pp-RPA is slightly larg...
-
accurate atomic quantum defects from particle particle Random Phase Approximation
arXiv: Chemical Physics, 2015Co-Authors: Yang Yang, Kieron Burke, Weitao YangAbstract:The accuracy of calculations of atomic Rydberg excitations cannot be judged by the usual measures, such as mean unsigned errors of many transitions. We show how to use quantum defect theory to (a) separate errors due to approximate ionization potentials, (b) extract smooth quantum defects to compare with experiment, and (c) quantify those defects with a few characteristic parameters. The particle-particle Random Phase Approximation (pp-RPA) produces excellent Rydberg transitions that are an order of magnitude more accurate than those of time-dependent density functional theory with standard Approximations. We even extract reasonably accurate defects from the lithium Rydberg series, despite the reference being open-shell. Our methodology can be applied to any Rydberg series of excitations with 4 transitions or more to extract the underlying threshold energy and characteristic quantum defect parameters. Our pp-RPA results set a demanding challenge for other excitation methods to match.
Gustavo E Scuseria - One of the best experts on this subject based on the ideXlab platform.
-
assessment of correlation energies based on the Random Phase Approximation
New Journal of Physics, 2012Co-Authors: Joachim Paier, Georg Kresse, Xinguo Ren, Patrick Rinke, Gustavo E Scuseria, Andreas Gruneis, Matthias SchefflerAbstract:The Random-Phase Approximation to the ground state correlation energy (RPA) in combination with exact exchange (EX) has brought the Kohn-Sham (KS) density functional theory one step closer towards a universal, 'general purpose first-principles method'. In an effort to systematically assess the influence of several correlation energy contributions beyond RPA, this paper presents dissociation energies of small molecules and solids, activation energies for hydrogen transfer and non-hydrogen transfer reactions, as well as reaction energies for a number of common test sets. We benchmark EX+RPA and several flavors of energy functionals going beyond it: second-order screened exchange (SOSEX), single-excitation (SE) corrections, renormalized single- excitation (rSE) corrections and their combinations. Both the SE correction and the SOSEX contribution to the correlation energy significantly improve on the notorious tendency of EX+RPA to underbind. Surprisingly, activation
-
assessment of correlation energies based on the Random Phase Approximation
arXiv: Materials Science, 2011Co-Authors: Joachim Paier, Georg Kresse, Xinguo Ren, Patrick Rinke, Gustavo E Scuseria, Andreas Grueneis, Matthias SchefflerAbstract:The Random-Phase Approximation to the ground state correlation energy (RPA) in combination with exact exchange (EX) has brought Kohn-Sham (KS) density functional theory one step closer towards a universal, "general purpose first principles method". In an effort to systematically assess the influence of several correlation energy contributions beyond RPA, this work presents dissociation energies of small molecules and solids, activation energies for hydrogen transfer and non-hydrogen transfer reactions, as well as reaction energies for a number of common test sets. We benchmark EX+RPA and several flavors of energy functionals going beyond it: second-order screened exchange (SOSEX), single excitation (SE) corrections, renormalized single excitation (rSE) corrections, as well as their combinations. Both the single excitation correction as well as the SOSEX contribution to the correlation energy significantly improve upon the notorious tendency of EX+RPA to underbind. Surprisingly, activation energies obtained using EX+RPA based on a KS reference alone are remarkably accurate. RPA+SOSEX+rSE provides an equal level of accuracy for reaction as well as activation energies and overall gives the most balanced performance, which makes it applicable to a wide range of systems and chemical reactions.
-
the connection between self interaction and static correlation a Random Phase Approximation perspective
Molecular Physics, 2010Co-Authors: Thomas M Henderson, Gustavo E ScuseriaAbstract:Semi-local density functional theory suggests a connection between static correlation and self-interaction. It is difficult to make such a connection from the wave function theory perspective, since few wave function methods permit self-interaction error. However, the Random Phase Approximation for ground-state correlation, which has a wave function derivation, does include self-interaction in its direct (Hartree) variant. This variant also describes left–right correlation. The self-interaction can be removed by means of second-order screened exchange; however, this also has negative consequences for the description of static correlation. This paper discusses the connection between the two concepts (static correlation and self-interaction) from the perspective provided by the Random Phase Approximation.
-
hybrid functionals including Random Phase Approximation correlation and second order screened exchange
Journal of Chemical Physics, 2010Co-Authors: Joachim Paier, Gustavo E Scuseria, Andreas Gruneis, Benjamin G Janesko, Thomas M Henderson, G KresseAbstract:There has been considerable recent interest in density functionals incorporating Random Phase Approximation (RPA) ground-state correlation. By virtue of its full nonlocality, RPA correlation is compatible with exact Hartree–Fock-type exchange and describes van der Waals interactions exceptionally well [B. G. Janesko et al., J. Chem. Phys. 130, 081105 (2009); J. Chem. Phys. 131, 034110 (2009)]. One caveat is that RPA correlation contains one-electron self-interaction error, which leads to disturbingly large correlation energies in the stretched bond situation of, e.g., H2+, He2+, or Ne2+. In the present work, we show that inclusion of second-order screened exchange rectifies the aforementioned failure of RPA correlation. We present a large number of molecular benchmark results obtained using full-range as well as long-range corrected hybrids incorporating second-order screened exchange correlation. This correction has a generally small, and sometimes undesirable, effect on RPA predictions for chemical prop...
-
hybrid functionals including Random Phase Approximation correlation and second order screened exchange
Journal of Chemical Physics, 2010Co-Authors: Joachim Paier, Gustavo E Scuseria, Andreas Gruneis, Benjamin G Janesko, Thomas M Henderson, Georg KresseAbstract:There has been considerable recent interest in density functionals incorporating Random Phase Approximation (RPA) ground-state correlation. By virtue of its full nonlocality, RPA correlation is compatible with exact Hartree-Fock-type exchange and describes van der Waals interactions exceptionally well [B. G. Janesko et al., J. Chem. Phys. 130, 081105 (2009); J. Chem. Phys. 131, 034110 (2009)]. One caveat is that RPA correlation contains one-electron self-interaction error, which leads to disturbingly large correlation energies in the stretched bond situation of, e.g., H(2)(+), He(2)(+), or Ne(2)(+). In the present work, we show that inclusion of second-order screened exchange rectifies the aforementioned failure of RPA correlation. We present a large number of molecular benchmark results obtained using full-range as well as long-range corrected hybrids incorporating second-order screened exchange correlation. This correction has a generally small, and sometimes undesirable, effect on RPA predictions for chemical properties, but appears to be very beneficial for the dissociation of H(2)(+), He(2)(+), and Ne(2)(+).
Dario Vretenar - One of the best experts on this subject based on the ideXlab platform.
-
stellar electron capture rates calculated with the finite temperature relativistic Random Phase Approximation
Physical Review C, 2011Co-Authors: Y F Niu, Nils Paar, Dario Vretenar, J MengAbstract:We introduce a self-consistent microscopic theoretical framework for modeling the process of electron capture on nuclei in stellar environment, based on relativistic energy density functionals. The finite-temperature relativistic mean-field model is used to calculate the single-nucleon basis and the occupation factors in a target nucleus, and Jπ=0±, 1±, and 2± charge- exchange transitions are described by the self-consistent finite- temperature relativistic Random-Phase Approximation. Cross sections and rates are calculated for electron capture on 54, 56Fe and 76, 78Ge in stellar environment, and results compared with predictions of similar and complementary model calculations.
-
quasiparticle Random Phase Approximation based on the relativistic hartree bogoliubov model ii nuclear spin and isospin excitations
Physical Review C, 2004Co-Authors: Nils Paar, Dario Vretenar, Tamara Niksic, P RingAbstract:The proton-neutron relativistic quasiparticle Random-Phase Approximation (PN-RQRPA) is formulated in the canonical single-nucleon basis of the relativistic Hartree-Bogoliubov model, for an effective Lagrangian characterized by density-dependent meson-nucleon couplings. The model includes both the T = 1 and T = 0 pairing channels. Pair configurations formed from the fully or partially occupied states of positive energy in the Fermi sea, and the empty negative-energy states from the Dirac sea, are included in PN-RQRPA configuration space. The model is applied to the analysis of charge-exchange modes: isobaric analog resonances and Gamow-Teller resonances.
-
quasiparticle Random Phase Approximation based on the relativistic hartree bogoliubov model
Physical Review C, 2003Co-Authors: Nils Paar, Dario Vretenar, P Ring, Tamara NiksicAbstract:The relativistic quasiparticle Random Phase Approximation (RQRPA) is formulated in the canonical single-nucleon basis of the relativistic Hartree-Bogoliubov (RHB) model. For the interaction in the particle-hole channel effective Lagrangians with nonlinear meson self-interactions are used, and pairing correlations are described by the pairing part of the finite-range Gogny interaction. The RQRPA configuration space includes the Dirac sea of negative-energy states. Both in the particle-hole and particle-particle channels, the same interactions are used in the RHB calculation of the ground state and in the matrix equations of the RQRPA. The RHB+RQRPA approach is tested in the example of multipole excitations of neutron-rich oxygen isotopes. The RQRPA is applied in the analysis of the evolution of the low-lying isovector dipole strength in Sn isotopes and $N=82$ isotones.
-
collectivity of the low lying dipole strength in relativistic Random Phase Approximation
Nuclear Physics, 2001Co-Authors: Nils Paar, Dario Vretenar, P Ring, G A LalazissisAbstract:Abstract The relativistic Random Phase Approximation is applied in the analysis of the evolution of the isovector dipole response in nuclei with a large neutron excess. The self-consistent framework of relativistic mean-field theory, which has been very successfully applied in the description of ground-state properties of nuclei far from the valley of β -stability, is extended to study the possible onset of low-energy collective isovector dipole modes in nuclei with extreme isospin values.
-
collectivity of the low lying dipole strength in relativistic Random Phase Approximation
arXiv: Nuclear Theory, 2001Co-Authors: Nils Paar, Dario Vretenar, P Ring, G A LalazissisAbstract:The relativistic Random Phase Approximation is applied in the analysis of the evolution of the isovector dipole response in nuclei with a large neutron excess. The self-consistent framework of relativistic mean-field theory, which has been very successfully applied in the description of ground-state properties of nuclei far from the valley of $\beta$-stability, is extended to study the possible onset of low-energy collective isovector dipole modes in nuclei with extreme isospin values.
F Simkovic - One of the best experts on this subject based on the ideXlab platform.
-
chiral two body currents and neutrinoless double β decay in the quasiparticle Random Phase Approximation
Physical Review C, 2014Co-Authors: J Engel, F Simkovic, P VogelAbstract:We test the effects of an approximate treatment of two-body contributions to the axial-vector current on the quasiparticle Random-Phase Approximation (QRPA) matrix elements for neutrinoless double-beta decay in a range of isotopes. The form and strength of the two-body terms come from chiral effective-field theory. The two-body currents typically reduce the matrix elements by about 20%, not as much as in shell-model calculations. One reason for the difference is that standard practice in the QRPA is to adjust the strength of the isoscalar pairing interaction to reproduce two-neutrino double-beta decay lifetimes. Another may be the larger QRPA single-particle space. Whatever the reasons, the effects on neutrinoless decay are significantly less than those on two-neutrino decay, both in the shell model and the QRPA.
-
0νββ and 2νββ nuclear matrix elements quasiparticle Random Phase Approximation and isospin symmetry restoration
Physical Review C, 2013Co-Authors: F Simkovic, Amand Faessler, Vadim Rodin, P VogelAbstract:Within the quasiparticle Random-Phase Approximation (QRPA) we achieve partial restoration of the isospin symmetry and hence fulfillment of the requirement that the 2νββ Fermi matrix element M^(2ν)_F vanishes, as it should, unlike in the previous version of the method. This is accomplished by separating the renormalization parameter g_pp of the particle-particle proton-neutron interaction into isovector and isoscalar parts. The isovector parameter g^(T=1)_(pp) needs to be chosen to be essentially equal to the pairing constant g_pair, so no new parameter is needed. For the 0νββ decay the Fermi matrix element M^(0ν)_F is substantially reduced, while the full matrix element M^(0ν) is reduced by ≈10%. We argue that this more consistent approach should be used from now on in the proton-neutron QRPA and in analogous methods
-
multi isotope degeneracy of neutrinoless double beta decay mechanisms in the quasi particle Random Phase Approximation
Physical Review D, 2011Co-Authors: Amand Faessler, G L Fogli, E Lisi, A M Rotunno, F SimkovicAbstract:We calculate nuclear matrix elements (NME) of neutrinoless double beta decay in four different candidate nuclei (Ge-76, Se-82, Mo-100, Te-130) within the quasiparticle Random Phase Approximation (QRPA) and its uncertainties. We assume (up to) four coexisting mechanisms for neutrinoless double beta decay, mediated by light Majorana neutrino exchange, heavy Majorana neutrino exchange, R-parity breaking supersymmetry, and squark-neutrino, interfering either constructively or destructively with each other. We find that, unfortunately, current NME uncertainties appear to prevent a robust determination of the relative contribution of each mechanism to the decay amplitude, even assuming accurate measurements of decay lifetimes. The near-degeneracy of the decay mechanisms is analyzed with simple algebraic techniques, which do not involve assumptions about the statistical distribution of errors. We discuss implications of such degeneracy on prospective searches for absolute neutrino masses.
-
multi isotope degeneracy of neutrinoless double β decay mechanisms in the quasiparticle Random Phase Approximation
Physical Review D, 2011Co-Authors: Amand Faessler, G L Fogli, E Lisi, A M Rotunno, F SimkovicAbstract:We calculate nuclear matrix elements of neutrinoless double beta decay ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) in four different candidate nuclei ($^{76}\mathrm{Ge}$, $^{82}\mathrm{Se}$, $^{100}\mathrm{Mo}$, $^{130}\mathrm{Te}$) within the quasiparticle Random Phase Approximation and its uncertainties. We assume (up to) four coexisting mechanisms for $0\ensuremath{\nu}2\ensuremath{\beta}$ decay, mediated by light Majorana neutrino exchange ($\ensuremath{\nu}$), heavy Majorana neutrino exchange ($N$), $R$-parity breaking supersymmetry ($\overline{)R}$), and squark-neutrino $(\stackrel{\texttildelow{}}{q})$, interfering either constructively or destructively with each other. We find that, unfortunately, current nuclear matrix element uncertainties appear to prevent a robust determination of the relative contribution of each mechanism to the decay amplitude, even assuming accurate measurements of decay lifetimes. The near-degeneracy of $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ mechanisms is analyzed with simple algebraic techniques, which do not involve assumptions about the statistical distribution of errors. We discuss implications of such degeneracy on prospective searches for absolute neutrino masses.
-
quasiparticle Random Phase Approximation uncertainties and their correlations in the analysis of 0 nu beta beta decay
Physical Review D, 2009Co-Authors: Amand Faessler, G L Fogli, E Lisi, Vadim Rodin, A M Rotunno, F SimkovicAbstract:The variances and covariances associated to the nuclear matrix elements of neutrinoless double beta decay ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) are estimated within the quasiparticle Random Phase Approximation. It is shown that correlated nuclear matrix elements uncertainties play an important role in the comparison of $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay rates for different nuclei, and that they are degenerate with the uncertainty in the reconstructed Majorana neutrino mass.
