The Experts below are selected from a list of 68343 Experts worldwide ranked by ideXlab platform
Laura Gagliardi - One of the best experts on this subject based on the ideXlab platform.
-
calculation of the zeeman effect for transition metal complexes by multiconfiguration Pair Density functional theory
Journal of Chemical Theory and Computation, 2021Co-Authors: Chen Zhou, Laura Gagliardi, Donald G. TruhlarAbstract:Spin-orbit coupling is especially critical for the description of magnetic anisotropy, electron paramagnetic resonance spectroscopy of inorganic radicals and transition-metal complexes, and intersystem crossing. Here, we show how spin-orbit coupling may be included in multiconfiguration Pair-Density functional theory (MC-PDFT), and we apply the resulting formulation to the calculation of magnetic g tensors (which govern the Zeeman effect) of molecules containing transition metals. MC-PDFT is an efficient method for including static and dynamic electronic correlation in the quantum mechanical treatment of molecules; here, we apply it with spin-orbit coupling by using complete active space self-consistent field (CASSCF) and complete active space configuration interaction (CASCI) wave functions and on-top Density functionals. We propose a systematic CASCI scheme for the g tensor calculation of the ground state of the systems under consideration, and we show its superiority over the conventional CASSCF scheme. State interaction, which is important for degenerate and nearly degenerate states, is included by extended multi-state PDFT (XMS-PDFT). Applications are reported for the ground doublet states of 25 transition-metal complexes with d1, d5, d7, and d9 configurations. The MC-PDFT methods are shown to be both efficient and accurate as compared with complete active space second-order perturbation theory.
-
localized active space Pair Density functional theory
Journal of Chemical Theory and Computation, 2021Co-Authors: Riddhish Pandharkar, Donald G. Truhlar, Christopher J. Cramer, Matthew R Hermes, Laura GagliardiAbstract:Accurate quantum chemical methods for the prediction of spin-state energy gaps for strongly correlated systems are computationally expensive and scale poorly with the size of the system. This makes calculations for many experimentally interesting molecules impractical even with abundant computational resources. Previous work has shown that the localized active space (LAS) self-consistent field (SCF) method can be an efficient way to obtain multiconfiguration SCF wave functions of comparable quality to the corresponding complete active space (CAS) ones. To obtain quantitative results, a post-SCF method is needed to estimate the complete correlation energy. One such method is multiconfiguration Pair-Density functional theory (PDFT), which calculates the energy based on the Density and on-top Pair Density obtained from a multiconfiguration wave function. In this work, we introduce localized-active-space PDFT, which uses a LAS wave function for subsequent PDFT calculations. The method is tested by computing spin-state energies and gaps in conjugated organic molecules and a bimetallic compound and comparing to the corresponding CAS-PDFT values.
-
analytic gradients for multiconfiguration Pair Density functional theory with Density fitting development and application to geometry optimization in the ground and excited states
Journal of Chemical Physics, 2021Co-Authors: Thais Scott, Donald G. Truhlar, Matthew R Hermes, Andrew M Sand, Roland Lindh, Meagan S Oakley, Laura GagliardiAbstract:Density fitting reduces the computational cost of both energy and gradient calculations by avoiding the computation and manipulation of four-index electron repulsion integrals. With this algorithm, one can efficiently optimize the geometries of large systems with an accurate multireference treatment. Here, we present the derivation of multiconfiguration Pair-Density functional theory for energies and analytic gradients with Density fitting. Six systems are studied, and the results are compared to those obtained with no approximation to the electron repulsion integrals and to the results obtained by complete active space second-order perturbation theory. With the new approach, there is an increase in the speed of computation with a negligible loss in accuracy. Smaller grid sizes have also been used to reduce the computational cost of multiconfiguration Pair-Density functional theory with little effect on the optimized geometries and gradient values.
-
localized active space Pair Density functional theory
ChemRxiv, 2021Co-Authors: Riddhish Pandharkar, Donald G. Truhlar, Christopher J. Cramer, Matthew R Hermes, Laura GagliardiAbstract:Accurate quantum chemical methods for the prediction of spin-state energy gaps for strongly correlated systems are computationally expensive and scale poorly with the size of the system. This makes calculations for many experimentally interesting molecules impractical even with abundant computational resources. In previous work, we have shown that the localized active space (LAS) self-consistent field (SCF) method is an efficient way to obtain multi-configuration SCF wave functions of comparable quality to the corresponding complete active space (CAS) ones. To obtain quantitative results, a post-SCF method is needed to estimate the complete correlation energy. One such method is multiconfiguration Pair-Density functional theory (PDFT), which calculates the energy based on the Density and on-top Pair Density obtained from a multiconfiguration wave function. In this work we introduce localized-active-space Pair-Density functional theory, which uses a LAS wave function for subsequent PDFT calculations. The method is tested for computing spin-state energy gaps in conjugated organic molecules and bimetallic compounds and is shown to give results within 0.05 eV of the corresponding CAS-PDFT results at a significantly lower cost.
-
a new mixing of nonlocal exchange and nonlocal correlation with multiconfiguration Pair Density functional theory
Journal of Physical Chemistry Letters, 2020Co-Authors: Riddhish Pandharkar, Donald G. Truhlar, Matthew R Hermes, Laura GagliardiAbstract:We propose a hybrid multiconfiguration Pair-Density functional theory (HMC-PDFT) that is a weighted average of complete-active-space self-consistent-field (CASSCF) and multiconfiguration Pair-densi...
Donald G. Truhlar - One of the best experts on this subject based on the ideXlab platform.
-
calculation of the zeeman effect for transition metal complexes by multiconfiguration Pair Density functional theory
Journal of Chemical Theory and Computation, 2021Co-Authors: Chen Zhou, Laura Gagliardi, Donald G. TruhlarAbstract:Spin-orbit coupling is especially critical for the description of magnetic anisotropy, electron paramagnetic resonance spectroscopy of inorganic radicals and transition-metal complexes, and intersystem crossing. Here, we show how spin-orbit coupling may be included in multiconfiguration Pair-Density functional theory (MC-PDFT), and we apply the resulting formulation to the calculation of magnetic g tensors (which govern the Zeeman effect) of molecules containing transition metals. MC-PDFT is an efficient method for including static and dynamic electronic correlation in the quantum mechanical treatment of molecules; here, we apply it with spin-orbit coupling by using complete active space self-consistent field (CASSCF) and complete active space configuration interaction (CASCI) wave functions and on-top Density functionals. We propose a systematic CASCI scheme for the g tensor calculation of the ground state of the systems under consideration, and we show its superiority over the conventional CASSCF scheme. State interaction, which is important for degenerate and nearly degenerate states, is included by extended multi-state PDFT (XMS-PDFT). Applications are reported for the ground doublet states of 25 transition-metal complexes with d1, d5, d7, and d9 configurations. The MC-PDFT methods are shown to be both efficient and accurate as compared with complete active space second-order perturbation theory.
-
localized active space Pair Density functional theory
Journal of Chemical Theory and Computation, 2021Co-Authors: Riddhish Pandharkar, Donald G. Truhlar, Christopher J. Cramer, Matthew R Hermes, Laura GagliardiAbstract:Accurate quantum chemical methods for the prediction of spin-state energy gaps for strongly correlated systems are computationally expensive and scale poorly with the size of the system. This makes calculations for many experimentally interesting molecules impractical even with abundant computational resources. Previous work has shown that the localized active space (LAS) self-consistent field (SCF) method can be an efficient way to obtain multiconfiguration SCF wave functions of comparable quality to the corresponding complete active space (CAS) ones. To obtain quantitative results, a post-SCF method is needed to estimate the complete correlation energy. One such method is multiconfiguration Pair-Density functional theory (PDFT), which calculates the energy based on the Density and on-top Pair Density obtained from a multiconfiguration wave function. In this work, we introduce localized-active-space PDFT, which uses a LAS wave function for subsequent PDFT calculations. The method is tested by computing spin-state energies and gaps in conjugated organic molecules and a bimetallic compound and comparing to the corresponding CAS-PDFT values.
-
analytic gradients for multiconfiguration Pair Density functional theory with Density fitting development and application to geometry optimization in the ground and excited states
Journal of Chemical Physics, 2021Co-Authors: Thais Scott, Donald G. Truhlar, Matthew R Hermes, Andrew M Sand, Roland Lindh, Meagan S Oakley, Laura GagliardiAbstract:Density fitting reduces the computational cost of both energy and gradient calculations by avoiding the computation and manipulation of four-index electron repulsion integrals. With this algorithm, one can efficiently optimize the geometries of large systems with an accurate multireference treatment. Here, we present the derivation of multiconfiguration Pair-Density functional theory for energies and analytic gradients with Density fitting. Six systems are studied, and the results are compared to those obtained with no approximation to the electron repulsion integrals and to the results obtained by complete active space second-order perturbation theory. With the new approach, there is an increase in the speed of computation with a negligible loss in accuracy. Smaller grid sizes have also been used to reduce the computational cost of multiconfiguration Pair-Density functional theory with little effect on the optimized geometries and gradient values.
-
localized active space Pair Density functional theory
ChemRxiv, 2021Co-Authors: Riddhish Pandharkar, Donald G. Truhlar, Christopher J. Cramer, Matthew R Hermes, Laura GagliardiAbstract:Accurate quantum chemical methods for the prediction of spin-state energy gaps for strongly correlated systems are computationally expensive and scale poorly with the size of the system. This makes calculations for many experimentally interesting molecules impractical even with abundant computational resources. In previous work, we have shown that the localized active space (LAS) self-consistent field (SCF) method is an efficient way to obtain multi-configuration SCF wave functions of comparable quality to the corresponding complete active space (CAS) ones. To obtain quantitative results, a post-SCF method is needed to estimate the complete correlation energy. One such method is multiconfiguration Pair-Density functional theory (PDFT), which calculates the energy based on the Density and on-top Pair Density obtained from a multiconfiguration wave function. In this work we introduce localized-active-space Pair-Density functional theory, which uses a LAS wave function for subsequent PDFT calculations. The method is tested for computing spin-state energy gaps in conjugated organic molecules and bimetallic compounds and is shown to give results within 0.05 eV of the corresponding CAS-PDFT results at a significantly lower cost.
-
a new mixing of nonlocal exchange and nonlocal correlation with multiconfiguration Pair Density functional theory
Journal of Physical Chemistry Letters, 2020Co-Authors: Riddhish Pandharkar, Donald G. Truhlar, Matthew R Hermes, Laura GagliardiAbstract:We propose a hybrid multiconfiguration Pair-Density functional theory (HMC-PDFT) that is a weighted average of complete-active-space self-consistent-field (CASSCF) and multiconfiguration Pair-densi...
Soumen Ghosh - One of the best experts on this subject based on the ideXlab platform.
-
generalized active space Pair Density functional theory an efficient method to study large strongly correlated conjugated systems
Chemical Science, 2017Co-Authors: Soumen Ghosh, Donald G. Truhlar, Christopher J. Cramer, Laura GagliardiAbstract:Predicting ground- and excited-state properties of open-shell organic molecules by electronic structure theory can be challenging because an accurate treatment has to correctly describe both static and dynamic electron correlation. Strongly correlated systems, i.e., systems with near-degeneracy correlation effects, are particularly troublesome. Multiconfigurational wave function methods based on an active space are adequate in principle, but it is impractical to capture most of the dynamic correlation in these methods for systems characterized by many active electrons. We recently developed a new method called multiconfiguration Pair-Density functional theory (MC-PDFT), that combines the advantages of wave function theory and Density functional theory to provide a more practical treatment of strongly correlated systems. Here we present calculations of the singlet–triplet gaps in oligoacenes ranging from naphthalene to dodecacene. Calculations were performed for unprecedently large orbitally optimized active spaces of 50 electrons in 50 orbitals, and we test a range of active spaces and active space partitions, including four kinds of frontier orbital partitions. We show that MC-PDFT can predict the singlet–triplet splittings for oligoacenes consistent with the best available and much more expensive methods, and indeed MC-PDFT may constitute the benchmark against which those other models should be compared, given the absence of experimental data.
-
multiconfiguration Pair Density functional theory is as accurate as caspt2 for electronic excitation
Journal of Physical Chemistry Letters, 2016Co-Authors: Chad E Hoyer, Soumen Ghosh, Donald G. Truhlar, Laura GagliardiAbstract:A correct description of electronically excited states is critical to the interpretation of visible–ultraviolet spectra, photochemical reactions, and excited-state charge-transfer processes in chemical systems. We have recently proposed a theory called multiconfiguration Pair-Density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory and a new kind of Density functional called an on-top Density functional. Here, we show that MC-PDFT with a first-generation on-top Density functional performs as well as CASPT2 for an organic chemistry database including valence, Rydberg, and charge-transfer excitations. The results are very encouraging for practical applications.
-
multiconfiguration Pair Density functional theory outperforms kohn sham Density functional theory and multireference perturbation theory for ground state and excited state charge transfer
Journal of Chemical Theory and Computation, 2015Co-Authors: Soumen Ghosh, Donald G. Truhlar, Andrew L Sonnenberger, Chad E Hoyer, Laura GagliardiAbstract:The correct description of charge transfer in ground and excited states is very important for molecular interactions, photochemistry, electrochemistry, and charge transport, but it is very challenging for Kohn–Sham (KS) Density functional theory (DFT). KS-DFT exchange-correlation functionals without nonlocal exchange fail to describe both ground- and excited-state charge transfer properly. We have recently proposed a theory called multiconfiguration Pair-Density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory with a new type of Density functional called an on-top Density functional. Here we have used MC-PDFT to study challenging ground- and excited-state charge-transfer processes by using on-top Density functionals obtained by translating KS exchange-correlation functionals. For ground-state charge transfer, MC-PDFT performs better than either the PBE exchange-correlation functional or CASPT2 wave function theory. For excited-state charge transfer, M...
-
multiconfiguration Pair Density functional theory outperforms kohn sham Density functional theory and multireference perturbation theory for ground state and excited state charge transfer
Journal of Chemical Theory and Computation, 2015Co-Authors: Soumen Ghosh, Donald G. Truhlar, Andrew L Sonnenberger, Chad E Hoyer, Laura GagliardiAbstract:The correct description of charge transfer in ground and excited states is very important for molecular interactions, photochemistry, electrochemistry, and charge transport, but it is very challenging for Kohn-Sham (KS) Density functional theory (DFT). KS-DFT exchange-correlation functionals without nonlocal exchange fail to describe both ground- and excited-state charge transfer properly. We have recently proposed a theory called multiconfiguration Pair-Density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory with a new type of Density functional called an on-top Density functional. Here we have used MC-PDFT to study challenging ground- and excited-state charge-transfer processes by using on-top Density functionals obtained by translating KS exchange-correlation functionals. For ground-state charge transfer, MC-PDFT performs better than either the PBE exchange-correlation functional or CASPT2 wave function theory. For excited-state charge transfer, MC-PDFT (unlike KS-DFT) shows qualitatively correct behavior at long-range with great improvement in predicted excitation energies.
Eduardo Fradkin - One of the best experts on this subject based on the ideXlab platform.
-
the physics of Pair Density waves cuprate superconductors and beyond
Annual Review of Condensed Matter Physics, 2020Co-Authors: D F Agterberg, Eduardo Fradkin, Steven A Kivelson, Patrick A Lee, J Seamus C Davis, Stephen D Edkins, Dale J Van Harlingen, Leo Radzihovsky, J M TranquadaAbstract:We review the physics of Pair-Density wave (PDW) superconductors. We begin with a macroscopic description that emphasizes order induced by PDW states, such as charge-Density wave, and discuss relat...
-
Pair Density wave order and Paired fractional quantum hall fluids
Physical Review X, 2019Co-Authors: Yuxuan Wang, Luiz Santos, Eduardo FradkinAbstract:A theoretical analysis provides new insight into how Majorana fermions behave in fractional quantum Hall systems, which, in turn, could lead to a better understanding of the interplay between topology and symmetry breaking in quantum matter.
-
Pair Density wave order and Paired fractional quantum hall fluids
arXiv: Strongly Correlated Electrons, 2018Co-Authors: Yuxuan Wang, Luiz Santos, Eduardo FradkinAbstract:The properties of the isotropic incompressible $\nu=5/2$ fractional quantum Hall (FQH) state are described by a Paired state of composite fermions in zero (effective) magnetic field, with a uniform $p_x+ip_y$ Pairing order parameter, which is a non-Abelian topological phase with chiral Majorana and charge modes at the boundary. Recent experiments suggest the existence of a proximate nematic phase at $\nu=5/2$. This finding motivates us to consider an inhomogeneous Paired state - a $p_x+ip_y$ Pair-Density-wave (PDW) - whose melting could be the origin of the observed liquid-crystalline phases. This state can viewed as an array of domain and anti-domain walls of the $p_x+i p_y$ order parameter. We show that the nodes of the PDW order parameter, the location of the domain walls (and anti-domain walls) where the order parameter changes sign, support a Pair of symmetry-protected counter-propagating Majorana modes. The coupling behavior of the domain wall Majorana modes crucially depends on the interplay of the Fermi energy $E_{F}$ and the PDW Pairing energy $E_{\textrm{pdw}}$. The analysis of this interplay yields a rich set of topological states. The Pair-Density-wave order state in Paired FQH system provides a fertile setting to study Abelian and non-Abelian FQH phases - as well as transitions thereof - tuned by the strength of the Paired liquid crystalline order.
-
Pair Density waves in superconducting vortex halos
Physical Review B, 2018Co-Authors: Yuxuan Wang, Eduardo Fradkin, Mohammad Hamidian, J Seamus C Davis, Stephen D Edkins, Steven A KivelsonAbstract:The authors analyze the interplay between a $d$-wave uniform superconducting and a Pair-Density-wave order (PDW) parameter in the neighborhood of a vortex, and compute the resulting local Density of states in the vortex halo. The intertwining of the two superconducting orders leads to a charge Density modulation with the same periodicity as the PDW, which is twice the period of the charge Density wave that arises as a second harmonic of the PDW itself. They discuss key features of the charge Density modulation that can be directly compared with recent results from scanning tunneling microscopy and speculate on the role PDW order may play in the global phase diagram of the hole-doped cuprates.
-
Pair Density wave correlations in the kondo heisenberg model
Physical Review Letters, 2010Co-Authors: Erez Berg, Eduardo Fradkin, Steven A KivelsonAbstract:We show, using Density-matrix renormalization-group calculations complemented by field-theoretic arguments, that the spin-gapped phase of the one dimensional Kondo-Heisenberg model exhibits quasi-long-range superconducting correlations only at a nonzero momentum. The local correlations in this phase resemble those of the Pair-Density-wave state which was recently proposed to describe the phenomenology of the striped ordered high-temperature superconductor ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ba}}_{x}{\mathrm{CuO}}_{4}$, in which the spin, charge, and superconducting orders are strongly intertwined.
Kieron Burke - One of the best experts on this subject based on the ideXlab platform.
-
escaping the symmetry dilemma through a Pair Density interpretation of spin Density functional theory
Physical Review A, 1995Co-Authors: John P Perdew, Andreas Savin, Kieron BurkeAbstract:In the standard interpretation of spin-Density functional theory, a self-consistent Kohn-Sham calculation within the local spin Density (LSD) or generalized gradient approximation (GGA) leads to a prediction of the total energy E, total electron Density n(r) =n~(r)+n ~(r), and spin magnetization Density m(r)=n~(r) — n~(r). This interpretation encounters a serious symmetry dilemma" for H2, Cr2, and many other molecules. Without changing LSD or GGA calculational methods and results, we escape this dilemma through an alternative interpretation in which the third physical prediction is not m (r) but the on-top electron Pair Density P(r, r), a quantity more directly related to the total energy in the absence of an external magnetic field. This alternative interpretation is also relevant to antiferromagnetic solids. We argue that the nonlocal exchange-correlation energy functional, which must be approximated, is most nearly local in the alternative spin-Density functional theory presented here, less so in the standard theory, and far less so in total-Density functional theory. Thus, in LSD or GGA, predictions of spin magnetization densities and moments are not so robust as predictions of total Density and energy. The alternative theory helps to explain the surprising accuracy of LSD and GGA energies, and suggests that the correct solution of the Kohn-Sham equations in LSD or GGA is the fully self-consistent broken-symmetry single determinant of lowest total energy.
-
escaping the symmetry dilemma through a Pair Density interpretation of spin Density functional theory
Physical Review A, 1995Co-Authors: John P Perdew, Andreas Savin, Kieron BurkeAbstract:In the standard interpretation of spin-Density functional theory, a self-consistent Kohn-Sham calculation within the local spin Density (LSD) or generalized gradient approximation (GGA) leads to a prediction of the total energy E, total electron Density n(r)=${\mathit{n}}_{\mathrm{\ensuremath{\uparrow}}}$(r)+${\mathit{n}}_{\mathrm{\ensuremath{\downarrow}}}$(r), and spin magnetization Density m(r)=${\mathit{n}}_{\mathrm{\ensuremath{\uparrow}}}$(r)-${\mathit{n}}_{\mathrm{\ensuremath{\downarrow}}}$(r). This interpretation encounters a serious ``symmetry dilemma'' for ${\mathrm{H}}_{2}$, ${\mathrm{Cr}}_{2}$, and many other molecules. Without changing LSD or GGA calculational methods and results, we escape this dilemma through an alternative interpretation in which the third physical prediction is not m(r) but the on-top electron Pair Density P(r,r), a quantity more directly related to the total energy in the absence of an external magnetic field. This alternative interpretation is also relevant to antiferromagnetic solids. We argue that the nonlocal exchange-correlation energy functional, which must be approximated, is most nearly local in the alternative spin-Density functional theory presented here, less so in the standard theory, and far less so in total-Density functional theory. Thus, in LSD or GGA, predictions of spin magnetization densities and moments are not so robust as predictions of total Density and energy. The alternative theory helps to explain the surprising accuracy of LSD and GGA energies, and suggests that the correct solution of the Kohn-Sham equations in LSD or GGA is the fully self-consistent broken-symmetry single determinant of lowest total energy.
