The Experts below are selected from a list of 39912 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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scaled opposite spin second order moller plesset Correlation Energy an economical Electronic structure method
2004Co-Authors: Yousung Jung, Rohini C Lochan, Anthony D Dutoi, Martin HeadgordonAbstract:A simplified approach to treating the Electron Correlation Energy is suggested in which only the α-β component of the second order Moller–Plesset Energy is evaluated, and then scaled by an empirical factor which is suggested to be 1.3. This scaled opposite-spin second order Energy (SOS-MP2), where MP2 is Moller–Plesset theory, yields results for relative energies and derivative properties that are statistically improved over the conventional MP2 method. Furthermore, the SOS-MP2 Energy can be evaluated without the fifth order computational steps associated with MP2 theory, even without exploiting any spatial locality. A fourth order algorithm is given for evaluating the opposite spin MP2 Energy using auxiliary basis expansions, and a Laplace approach, and timing comparisons are given.
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an accurate local model for triple substitutions in fourth order moller plesset theory and in perturbative corrections to singles and doubles coupled cluster methods
2000Co-Authors: Paul E Maslen, Michael S Lee, Martin HeadgordonAbstract:Abstract Two noniterative local models for evaluating the contribution of triple substitutions to the Electron Correlation Energy (as needed in MP4 and CCSD(T)), are developed. The occupied space is spanned by a minimal basis, and the virtual space by an extended basis of atom-centered functions. The triple substitutions are truncated by an atomic criterion such that either zero or one Electrons can be transferred between atoms. The covalent model asymptotically recovers 70% of the triples Correlation Energy for poly-ynes with a 6-31G* basis, while the singly-ionic model recovers 99%.
Paul L A Popelier - One of the best experts on this subject based on the ideXlab platform.
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atomic partitioning of the mpn n 2 3 4 dynamic Electron Correlation Energy by the interacting quantum atoms method a fast and accurate electrostatic potential integral approach
2019Co-Authors: Mark A Vincent, Arnaldo F Silva, Paul L A PopelierAbstract:Recently, the quantum topological Energy partitioning method called interacting quantum atoms (IQA) has been extended to MPn (n = 2, 3, 4) wave functions. This enables the extraction of chemical insight related to dynamic Electron Correlation. The large computational expense of the IQA-MPn approach is compensated by the advantages that IQA offers compared to older nontopological Energy decomposition schemes. This expense is problematic in the construction of a machine learning training set to create kriging models for topological atoms. However, the algorithm presented here markedly accelerates the calculation of atomically partitioned Electron Correlation energies. Then again, the algorithm cannot calculate pairwise interatomic energies because it applies analytical integrals over whole space (rather than over atomic volumes). However, these pairwise energies are not needed in the quantum topological force field FFLUX, which only uses the Energy of an atom interacting with all remaining atoms of the system that it is part of. Thus, it is now feasible to generate accurate and sizeable training sets at MPn level of theory. © 2019 The Authors. Journal of Computational Chemistry published by Wiley Periodicals, Inc.
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partitioning dynamic Electron Correlation Energy viewing moller plesset Correlation energies through interacting quantum atom iqa Energy partitioning
2016Co-Authors: James L Mcdonagh, Mark A Vincent, Paul L A PopelierAbstract:Abstract Here MP2, MP3 and MP4(SDQ) are Energy-partitioned for the first time within the Interacting Quantum Atoms (IQA) context, as proof-of-concept for H2, He2 and HF. Energies are decomposed into four primary Energy contributions: (i) atomic self-energies, and atomic interaction energies comprising of (ii) Coulomb, (iii) exchange and (iv) dynamic election Correlation terms. We generate and partition one- and two-particle density-matrices to obtain all atomic Energy components. This work suggests that, in terms of Van der Waals dispersion, the Correlation energies represent an atomic stabilisation, by proximity to other atoms, as opposed to direct interactions with other nearby atoms.
Yuzhi Song - One of the best experts on this subject based on the ideXlab platform.
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accurate global potential Energy surface for the ground state of ch2 by extrapolation to the complete basis set limit
2018Co-Authors: Lu Guo, Lulu Zhang, Yuzhi SongAbstract:A full three-dimensional global potential Energy surface is reported for the ground state of CH2+ by fitting accurate multireference configuration interaction energies calculated using aug-cc-pVQZ and aug-cc-pV5Z basis sets with extrapolation of the Electron Correlation Energy to the complete basis set limit. The topographical characteristics have been compared in detail with a potential Energy surface of the same type recently reported [J. Chem. Phys., 2015, 142, 124302] based on a least-squares fit to accurate high level ab initio MRCI(Q) energies, calculated using AV6Z basis set. The new three-dimensional global potential Energy surface is then used in quasiclassical trajectory calculations for H(2S) + CH+(X1Σ+) → C+(2P) + H2(X1Σg+) reaction. The integral cross sections, differential cross sections and the rate coefficients have been computed. A comparison shows that our potential Energy surface can be applied to any type of dynamic study.
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accurate adiabatic potential Energy surface for 12a state of fh2 based on ab initio data extrapolated to the complete basis set limit
2015Co-Authors: Yuzhi Song, A J C VarandasAbstract:An accurate single-sheeted double many-body expansion potential Energy surface is reported for the title system. It is obtained by using the aug-cc-pVTZ and aug-cc-pVQZ basis sets with extrapolation of the Electron Correlation Energy to the complete basis set limit, plus extrapolation to the complete basis set limit of the complete-active-space self-consistent field Energy. The collinear and bending barrier heights of the new global potential Energy surface is 2.301 and 1.768 kcal mol-1, in very good agreement with the values of 2.222 and 1.770 kcal mol-1 from the current best potential Energy surface. In particular, the new potential Energy surface describes well the important van der Waals interactions which is very useful for investigating the dynamics of the title system. Thus, the new potential Energy surface can both be recommended for dynamics studies of the F + H2 reaction and as building block for constructing the potential Energy surfaces of larger fluorine/hydrogen containing systems. Based on the new potential Energy surface, a preliminary theoretical study of the reaction F(2P) + H2 (X1 Σ g +) → FH(X 1 Σ +) + H(2S) has been carried out with the methods of quasi-classical trajectory and quantum mechanical. The results have shown that the new PES is suitable for any kind of dynamics studies.
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accurate ab initio double many body expansion potential Energy surface for ground state h2s by extrapolation to the complete basis set limit
2009Co-Authors: Yuzhi Song, A J C VarandasAbstract:A single-sheeted potential Energy surface is reported for the Electronic ground-state of H2S by fitting accurate multireference configuration interaction energies calculated using aug-cc-pVTZ and aug-cc-pVQZ basis sets with extrapolation of the Electron Correlation Energy to the complete basis set limit, plus extrapolation to the complete basis set limit of the complete-active-space self-consistent field Energy. A switching function formalism has been used to warrant the correct behavior at the H2(X Σ1g+)+S(D1) and SH(X Π2)+H(S2) dissociation limits. The topographical features of the novel global potential Energy surface are examined in detail, with the former being used for exploratory quasiclassical trajectory calculations of the thermal rate constant for the S(D1)+H2, S(D1)+D2, and S(D1)+HD reactions at room temperature. A comparison with other available potential Energy surfaces as well as kinetics data is also provided.
A J C Varandas - One of the best experts on this subject based on the ideXlab platform.
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accurate adiabatic potential Energy surface for 12a state of fh2 based on ab initio data extrapolated to the complete basis set limit
2015Co-Authors: Yuzhi Song, A J C VarandasAbstract:An accurate single-sheeted double many-body expansion potential Energy surface is reported for the title system. It is obtained by using the aug-cc-pVTZ and aug-cc-pVQZ basis sets with extrapolation of the Electron Correlation Energy to the complete basis set limit, plus extrapolation to the complete basis set limit of the complete-active-space self-consistent field Energy. The collinear and bending barrier heights of the new global potential Energy surface is 2.301 and 1.768 kcal mol-1, in very good agreement with the values of 2.222 and 1.770 kcal mol-1 from the current best potential Energy surface. In particular, the new potential Energy surface describes well the important van der Waals interactions which is very useful for investigating the dynamics of the title system. Thus, the new potential Energy surface can both be recommended for dynamics studies of the F + H2 reaction and as building block for constructing the potential Energy surfaces of larger fluorine/hydrogen containing systems. Based on the new potential Energy surface, a preliminary theoretical study of the reaction F(2P) + H2 (X1 Σ g +) → FH(X 1 Σ +) + H(2S) has been carried out with the methods of quasi-classical trajectory and quantum mechanical. The results have shown that the new PES is suitable for any kind of dynamics studies.
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accurate ab initio based double many body expansion adiabatic potential Energy surface for the 22 a state of nh2 by extrapolation to the complete basis set limit
2012Co-Authors: A J C VarandasAbstract:An accurate single-sheeted double many-body expansion potential Energy surface (PES) is reported for the title system, which is suitable for dynamics and kinetics studies of the reactions N(2D) + H2(X1 Σ) ⇋ NH(b1 Σ+) + H(2S) and their isotopomeric variants. It is obtained using the aug-cc-pVTZ and aug-cc-pVQZ basis sets with extrapolation of the Electron Correlation Energy to the complete basis set limit, plus extrapolation to the complete basis set limit of the complete-active-space self-consistent field Energy. A switching function formalism has been used to ensure the correct behavior at the NH(A3 Π) + H(2S) and NH(b1 Σ+) + H(2S) dissociation limits. The topographical features of the new global PES are examined in detail, and found to be in general good agreement with those calculated directly from the raw ab initio energies, as well as previous calculations from the literature. © 2012 Wiley Periodicals, Inc.
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accurate ab initio double many body expansion potential Energy surface for ground state h2s by extrapolation to the complete basis set limit
2009Co-Authors: Yuzhi Song, A J C VarandasAbstract:A single-sheeted potential Energy surface is reported for the Electronic ground-state of H2S by fitting accurate multireference configuration interaction energies calculated using aug-cc-pVTZ and aug-cc-pVQZ basis sets with extrapolation of the Electron Correlation Energy to the complete basis set limit, plus extrapolation to the complete basis set limit of the complete-active-space self-consistent field Energy. A switching function formalism has been used to warrant the correct behavior at the H2(X Σ1g+)+S(D1) and SH(X Π2)+H(S2) dissociation limits. The topographical features of the novel global potential Energy surface are examined in detail, with the former being used for exploratory quasiclassical trajectory calculations of the thermal rate constant for the S(D1)+H2, S(D1)+D2, and S(D1)+HD reactions at room temperature. A comparison with other available potential Energy surfaces as well as kinetics data is also provided.
Xinguo Ren - One of the best experts on this subject based on the ideXlab platform.
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renormalized second order perturbation theory for the Electron Correlation Energy concept implementation and benchmarks
2013Co-Authors: Xinguo Ren, Patrick Rinke, Gustavo E Scuseria, Matthias SchefflerAbstract:We present a renormalized second-order perturbation theory (rPT2), based on a Kohn-Sham (KS) reference state, for the Electron Correlation Energy that includes the random-phase approximation (RPA), second-order screened exchange (SOSEX), and renormalized single excitations (rSE). These three terms all involve a summation of certain types of diagrams to infinite order, and can be viewed as "renormalization "o f the second-order direct, exchange, and single-excitation (SE) terms of Rayleigh-Schrperturbation theory based on a KS reference. In this work, we establish the concept of rPT2 and present the numerical details of our SOSEX and rSE implementations. A preliminary version of rPT2, in which the renormalized SE (rSE) contribution was treated approximately, has already been benchmarked for molecular atomization energies and chemical reaction barrier heights and shows a well-balanced performance (J. Paieret al.,New J. Phys.14, 043002 (2012)). In this work, we present a refined version of rPT2, in which we evaluate the rSE series of diagrams rigorously. We then extend the benchmark studies to noncovalent interactions, including the rare-gas dimers, and the S22 and S66 test sets, as well as the cohesive Energy of small copper clusters, and the equilibrium geometry of 10 diatomic molecules. Despite some remaining shortcomings, we conclude that rPT2 gives an overall satisfactory performance across different Electronic situations, and is a promising step towards a generally applicable Electronic-structure approach.
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renormalized second order perturbation theory for the Electron Correlation Energy concept implementation and benchmarks
2012Co-Authors: Xinguo Ren, Patrick Rinke, Gustavo E Scuseria, Matthias SchefflerAbstract:We present a renormalized second-order perturbation theory (rPT2), based on a Kohn-Sham (KS) reference state, for the Electron Correlation Energy that includes the random-phase approximation (RPA), second-order screened exchange (SOSEX), and renormalized single excitations (rSE). These three terms all involve a summation of certain types of diagrams to infinite order, and can be viewed as "renormalization" of the 2nd-order direct, exchange, and single excitation (SE) terms of Rayleigh-Schrodinger perturbation theory based on an KS reference. In this work we establish the concept of rPT2 and present the numerical details of our SOSEX and rSE implementations. A preliminary version of rPT2, in which the renormalized SE (rSE) contribution was treated approximately, has already been benchmarked for molecular atomization energies and chemical reaction barrier heights and shows a well balanced performance [Paier et al, New J. Phys. 14, 043002 (2012)]. In this work, we present a refined version of rPT2, in which we evaluate the rSE series of diagrams rigorously. We then extend the benchmark studies to non-covalent interactions, including the rare-gas dimers, and the S22 and S66 test sets. Despite some remaining shortcomings, we conclude that rPT2 gives an overall satisfactory performance across different chemical environments, and is a promising step towards a generally applicable Electronic structure approach.
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beyond the random phase approximation for the Electron Correlation Energy the importance of single excitations
2011Co-Authors: Xinguo Ren, Patrick Rinke, Alexandre Tkatchenko, Matthias SchefflerAbstract:The random-phase approximation (RPA) for the Electron Correlation Energy, combined with the exact-exchange (EX) Energy, represents the state-of-the-art exchange-Correlation functional within density-functional theory. However, the standard RPA practice---evaluating both the EX and the RPA Correlation energies using Kohn-Sham (KS) orbitals from local or semilocal exchange-Correlation functionals---leads to a systematic underbinding of molecules and solids. Here we demonstrate that this behavior can be corrected by adding a ``single excitation'' contribution, so far not included in the standard RPA scheme. A similar improvement can also be achieved by replacing the non-self-consistent EX total Energy by the corresponding self-consistent Hartree-Fock total Energy, while retaining the RPA Correlation Energy evaluated using KS orbitals. Both schemes achieve chemical accuracy for a standard benchmark set of noncovalent intermolecular interactions.