The Experts below are selected from a list of 75 Experts worldwide ranked by ideXlab platform
Martin Kaupp - One of the best experts on this subject based on the ideXlab platform.
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computation of nmr shifts for paramagnetic solids including zero field splitting and beyond dft approaches application to limpo4 m mn fe co ni and mpo4 m fe co
Journal of Physical Chemistry C, 2019Co-Authors: Arobendo Mondal, Martin KauppAbstract:A protocol for the computation of NMR shifts of paramagnetic spin-coupled solids is described and applied to the olivine-type lithium-ion battery cathode materials LiMPO4 (M = Mn, Fe, Co, Ni) and to the related binary phosphates MPO4 (M = Fe, Co). The computational approach includes Fermi-contact (FC), pseudocontact (PC), as well as orbital contributions to the shifts and combines periodic density functional computations with multireference Post-Hartree–Fock Methods. A shift formalism based on EPR spin-Hamiltonian parameters corrected for residual spin couplings within the Curie–Weiss regime is used. Orbital shieldings as well as hyperfine couplings (HFCs) are obtained at DFT levels for large simulation cells using the CP2K code, taking advantage of hybrid functionals for the HFCs. g-Tensors and zero-field-splitting tensors are computed within an incremental cluster model, using CASSCF and NEVPT2 approaches, providing thus the first Post-Hartree–Fock treatments of these properties for extended solids. Com...
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hyperfine coupling constants of the nitrogen and phosphorus atoms a challenge for exact exchange density functional and Post hartree fock Methods
Journal of Chemical Physics, 2010Co-Authors: Martin Kaupp, Andreas Heselmann, A.v. Arbuznikov, Andreas GörlingAbstract:The isotropic hyperfine coupling constants of the free N(S4) and P(S4) atoms have been evaluated with high-level Post-Hartree–Fock and density-functional Methods. The phosphorus hyperfine coupling presents a significant challenge to both types of Methods. With large basis sets, MP2 and coupled-cluster singles and doubles calculations give much too small values for the phosphorus atom. Triple excitations are needed in coupled-cluster calculations to achieve reasonable agreement with experiment. None of the standard density functionals reproduce even the correct sign of this hyperfine coupling. Similarly, the computed hyperfine couplings depend crucially on the self-consistent treatment in exact-exchange density-functional theory within the optimized effective potential (OEP) method. Well-balanced auxiliary and orbital basis sets are needed for basis-expansion exact-exchange-only OEP approaches to come close to Hartree–Fock or numerical OEP data. Results from the localized Hartree–Fock and Krieger–Li–Iafrat...
Ugur Bozkaya - One of the best experts on this subject based on the ideXlab platform.
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derivation of general analytic gradient expressions for density fitted Post hartree fock Methods an efficient implementation for the density fitted second order moller plesset perturbation theory
Journal of Chemical Physics, 2014Co-Authors: Ugur BozkayaAbstract:General analytic gradient expressions (with the frozen-core approximation) are presented for density-fitted Post-HF Methods. An efficient implementation of frozen-core analytic gradients for the second-order Moller–Plesset perturbation theory (MP2) with the density-fitting (DF) approximation (applying to both reference and correlation energies), which is denoted as DF-MP2, is reported. The DF-MP2 method is applied to a set of alkanes, conjugated dienes, and noncovalent interaction complexes to compare the computational cost of single point analytic gradients with MP2 with the resolution of the identity approach (RI-MP2) [F. Weigend and M. Haser, Theor. Chem. Acc. 97, 331 (1997); R. A. Distasio, R. P. Steele, Y. M. Rhee, Y. Shao, and M. Head-Gordon, J. Comput. Chem. 28, 839 (2007)]. In the RI-MP2 method, the DF approach is used only for the correlation energy. Our results demonstrate that the DF-MP2 method substantially accelerate the RI-MP2 method for analytic gradient computations due to the reduced inpu...
Jeanluc Bredas - One of the best experts on this subject based on the ideXlab platform.
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benchmarking Post hartree fock Methods to describe the nonlinear optical properties of polymethines an investigation of the accuracy of algebraic diagrammatic construction adc approaches
Journal of Chemical Theory and Computation, 2016Co-Authors: Stefan Knippenberg, Rebecca L Gieseking, Dirk R Rehn, Sukrit Mukhopadhyay, Andreas Dreuw, Jeanluc BredasAbstract:Third-order nonlinear optical (NLO) properties of polymethine dyes have been widely studied for applications such as all-optical switching. However, the limited accuracy of the current computational methodologies has prevented a comprehensive understanding of the nature of the lowest excited states and their influence on the molecular optical and NLO properties. Here, attention is paid to the lowest excited-state energies and their energetic ratio, as these characteristics impact the figure-of-merit for all-optical switching. For a series of model polymethines, we compare several algebraic diagrammatic construction (ADC) schemes for the polarization propagator with approximate second-order coupled cluster (CC2) theory, the widely used INDO/MRDCI approach and the symmetry-adapted cluster configuration interaction (SAC-CI) algorithm incorporating singles and doubles linked excitation operators (SAC-CI SD-R). We focus in particular on the ground-to-excited state transition dipole moments and the correspondin...
Andreas Görling - One of the best experts on this subject based on the ideXlab platform.
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hyperfine coupling constants of the nitrogen and phosphorus atoms a challenge for exact exchange density functional and Post hartree fock Methods
Journal of Chemical Physics, 2010Co-Authors: Martin Kaupp, Andreas Heselmann, A.v. Arbuznikov, Andreas GörlingAbstract:The isotropic hyperfine coupling constants of the free N(S4) and P(S4) atoms have been evaluated with high-level Post-Hartree–Fock and density-functional Methods. The phosphorus hyperfine coupling presents a significant challenge to both types of Methods. With large basis sets, MP2 and coupled-cluster singles and doubles calculations give much too small values for the phosphorus atom. Triple excitations are needed in coupled-cluster calculations to achieve reasonable agreement with experiment. None of the standard density functionals reproduce even the correct sign of this hyperfine coupling. Similarly, the computed hyperfine couplings depend crucially on the self-consistent treatment in exact-exchange density-functional theory within the optimized effective potential (OEP) method. Well-balanced auxiliary and orbital basis sets are needed for basis-expansion exact-exchange-only OEP approaches to come close to Hartree–Fock or numerical OEP data. Results from the localized Hartree–Fock and Krieger–Li–Iafrat...
Daniel A Boese - One of the best experts on this subject based on the ideXlab platform.
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assessment of coupled cluster theory and more approximate Methods for hydrogen bonded systems
Journal of Chemical Theory and Computation, 2013Co-Authors: Daniel A BoeseAbstract:To assess the accuracy of Post-Hartree-Fock Methods like CCSD(T), MP3, MP2.5, MP2, SCS-MP2, SOS-MP2, and DFT-SAPT, we evaluated several effects going beyond valence-correlated CCSD(T). For 16 small hydrogen bonded systems, CCSD(T) achieves an RMS error of 0.17 kJ/mol in the dissociation energy compared to our best estimate, which is a composite method akin to W4 theory. The error of CCSD(T) is thus much lower than for atomization energies. MP2 is surprisingly accurate for these systems with an RMS error of 1.3 kJ/mol. MP2.5 yields a clear improvement over MP2 (RMS of 0.5 kJ/mol) but still has an error about 3 times as large as CCSD(T) for the absolute RMS and almost 10 times as large for the relative RMS error. Neither SCS-MP2, SOS-MP2, nor DFT-SAPT yield lower errors than MP2. With a ΔCCSD(T) correction to MP2, the basis set limit is readily achieved when employing diffuse functions-without these, the convergence is rather slow.