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Jurgen Gauss - One of the best experts on this subject based on the ideXlab platform.

  • on the convergence of perturbative coupled cluster triples expansions error cancellations in the ccsd t model and the importance of amplitude relaxation
    Journal of Chemical Physics, 2015
    Co-Authors: Janus J Eriksen, Poul Jorgensen, Jurgen Gauss
    Abstract:

    Recently, we proposed a novel Lagrangian–based perturbation series—the CCSD(T–n) series—which systematically corrects the coupled cluster singles and doubles (CCSD) energy in orders of the Moller-Plesset fluctuation potential for effects due to triple excitations. In the present study, we report numerical results for the CCSD(T–n) series up through fourth order which show the predicted convergence trend throughout the series towards the energy of its target, the coupled cluster singles, doubles, and triples (CCSDT) model. Since effects due to the relaxation of the CCSD singles and doubles amplitudes enter the CCSD(T–n) series at fourth order (the CCSD(T–4) model), we are able to separate these effects from the total energy correction and thereby emphasize their crucial importance. Furthermore, we illustrate how the ΛCCSD[T]/(T) and CCSD[T]/(T) models, which in slightly different manners augment the CCSD energy by the [T] and (T) corrections rationalized from many-body perturbation theory, may be viewed as approximations to the second-order CCSD(T–2) model. From numerical comparisons with the CCSD(T–n) models, we show that the extraordinary performance of the ΛCCSD[T]/(T) and CCSD[T]/(T) models relies on fortuitous, yet rather consistent, cancellations of errors. As a side product of our investigations, we are led to reconsider the asymmetric ΛCCSD[T] model due to both its rigorous theoretical foundation and its performance, which is shown to be similar to that of the CCSD(T) model for systems at equilibrium geometry and superior to it for distorted systems. In both the calculations at equilibrium and distorted geometries, however, the ΛCCSD[T] and CCSD(T) models are shown to be outperformed by the fourth-order CCSD(T–4) model.

  • a lagrangian framework for deriving triples and quadruples corrections to the ccsd energy
    Journal of Chemical Physics, 2014
    Co-Authors: Janus J Eriksen, Poul Jorgensen, Kasper Kristensen, Thomas Kjaergaard, Jurgen Gauss
    Abstract:

    Using the coupled cluster Lagrangian technique, we have determined perturbative corrections to the coupled cluster singles and doubles (CCSD) energy that converge towards the coupled cluster singles, doubles, and triples (CCSDT) and coupled cluster singles, doubles, triples, and quadruples (CCSDTQ) energies, considering the CCSD state as the unperturbed reference state and the fluctuation potential as the perturbation. Since the Lagrangian technique is utilized, the energy corrections satisfy Wigner's 2n + 1 rule for the cluster amplitudes and the 2n + 2 rule for the Lagrange multipliers. The energy corrections define the CCSD perturbation series, CCSD(T–n) and CCSD(TQ–n), which are term-wise size extensive to any order in the perturbation. A detailed comparison of the CCSD(TQ–n) series and the CC(2)PT(n) series of Hirata et al. [J. Chem. Phys. 114, 3919 (2001)] has been performed, revealing some deficiencies of the latter related to the target energy of the series and its lack of size extensivity.

  • quantitative prediction of gas phase 13c nuclear magnetic shielding constants
    Journal of Chemical Physics, 2003
    Co-Authors: Alexander A Auer, Jurgen Gauss, John F Stanton
    Abstract:

    Benchmark calculations of F19 nuclear magnetic shielding constants are presented for a set of 28molecules. Near-quantitative accuracy (ca. 2ppm deviation from experiment) is achieved if (1) electron correlation is adequately treated by employing the coupled-cluster singles and doubles (CCSD) model augmented by a perturbative correction for triple excitations [CCSD(T)], (2) large (uncontracted) basis sets are used, (3) gauge-including atomic orbitals are used to ensure gauge-origin independence, (4) calculations are performed at accurate equilibrium geometries [obtained from CCSD(T)/cc-pVTZ calculations correlating all electrons], and (5) vibrational averaging and temperature corrections via second-order vibrational perturbation theory (VPT2) are included. For the CCSD(T)/13s9p4d3f calculations corrected for vibrational effects, mean and standard deviation from experiment are −1.9 and 1.6ppm, respectively. Less elaborate theoretical treatments result in larger errors. Consideration of relative shifts can r...

  • perturbative treatment of the similarity transformed hamiltonian in equation of motion coupled cluster approximations
    Journal of Chemical Physics, 1995
    Co-Authors: John F Stanton, Jurgen Gauss
    Abstract:

    A series of size‐consistent approximations to the equation‐of‐motion coupled cluster method in the singles and doubles approximation (EOM‐CCSD) are developed by subjecting the similarity transformed Hamiltonian H=exp(−T)H exp(T) to a perturbation expansion. Attention is directed to N and N−1 electron final state realizations of the method defined by truncation of H at second order. Explicit spin–orbital equations for the energy and its first derivative are documented for both approaches [EOMEE‐CCSD(2) and EOMIP‐CCSD(2), respectively], and have been implemented in a large‐scale quantum chemistry program. Vertical ionization potentials calculated by EOMIP‐CCSD(2) are shown to be equivalent to those of an approach presented recently by Nooijen and Snijders [J. Chem. Phys. 102, 1681 (1995)]. Applications of both EOMIP‐CCSD(2) and EOMEE‐CCSD(2) provide results for final state properties that compare favorably with those obtained in full EOM‐CCSD calculations. Analysis of the computational aspects of the approximate and full EOM‐CCSD methods shows that the cost of EOMIP‐CCSD(2) energy and gradient calculations scales in proportion to the fifth power of the basis set size, a significant savings over the sixth power dependence of EOMIP‐CCSD. This feature is of great practical importance, as it shows that this N−1 electron final state approach has a large domain of applicability and is therefore likely to become a valuable tool for application calculations. On the other hand, the same cannot be said for EOMEE‐CCSD(2) since its asymptotic computational dependence and storage requirements are the same as the full EOMEE‐CCSD method.

  • a ccsd t investigation of carbonyl oxide and dioxirane equilibrium geometries dipole moments infrared spectra heats of formation and isomerization energies
    Chemical Physics Letters, 1993
    Co-Authors: Dieter Cremer, Jurgen Gauss, Elfi Kraka, John F Stanton, Rodney J Bartlett
    Abstract:

    Abstract A CCSD and CCSD (T) investigation of carbonyl oxide (1) and its cyclic isomer dioxirane (2) has been carried out employing DZ + P and TZ + 2P basis sets. Calculated geometries, charge distributions, and dipole moments suggest that 1 possesses more zwitterionic character (CCSD (T) dipole moment 4 D) than has been predicted. 1 can be distinguished from 2 by its infrared spectrum as indicated by CCSD (T) frequencies, intensities, and isotopic shifts. The heats of formation ΔH0f (298) for 1 and 2 are 30.2 and 6.0 kcal/mol, respectively; the CCSD (T) barrier to isomerization from 1 to 2 is 19.2 kcal/mol. Decomposition of 1 and 2 can lead to CO, CO2, H2O, H2 but not to free CH2, O2 or O. Both isomers should be powerful epoxidation agents in the presence of alkenes, but they should differ in their ability to form cyclopropanes with alkenes.

Henry F. Schaefer - One of the best experts on this subject based on the ideXlab platform.

  • the singlet electronic ground state isomers of dialuminum monoxide aloal alalo and the transition state connecting them
    Journal of Chemical Physics, 2005
    Co-Authors: Justin M Turney, Yukio Yamaguchi, Levent Sari, Henry F. Schaefer
    Abstract:

    The singlet electronic ground state isomers, XΣg+1 (AlOAl D∞h) and XΣ+1 (AlAlO C∞ν), of dialuminum monoxide have been systematically investigated using ab initio electronic structure theory. The equilibrium structures and physical properties for the two molecules have been predicted employing self-consistent field (SCF) configuration interaction with single and double excitations (CISD), multireference CISD (MRCISD), coupled cluster with single and double excitations (CCSD), CCSD with perturbative triples [CCSD(T)], CCSD with iterative partial triple excitations (CCSDT-3 and CC3), and full triples (CCSDT) coupled cluster methods. Four correlation consistent polarized valence (cc-pVXZ) type basis sets were used. The AlAlO system is rather challenging theoretically. The two isomers are confirmed to have linear structures at all levels of theory. The symmetric isomer AlOAl is predicted to lie 81.9kcalmol−1 below the asymmetric isomer AlAlO at the cc-pV(Q+d)Z CCSD(T) level of theory. The predicted harmonic ...

  • the sioh hsio system a high level quantum mechanical study
    Journal of Chemical Physics, 1996
    Co-Authors: Yukio Yamaguchi, Yaoming Xie, Seungjoon Kim, Henry F. Schaefer
    Abstract:

    The potential energy hypersurface of the SiOH–HSiO system has been investigated using ab initio electronic structure theory. The geometries and physical properties including dipole moments, harmonic vibrational frequencies, and associated infrared (IR) intensities for the two equilibrium and isomerization (1,2 hydrogen shift) transition state structures have been determined employing self‐consistent‐field (SCF) and configuration interaction with single and double excitations (CISD) methods. At the CISD optimized geometries, single point energies of the three stationary points were evaluated using coupled cluster with single and double excitations (CCSD) and CCSD with perturbative triple excitations [CCSD(T)] levels of theory. In the correlated procedures three different frozen core schemes (6 frozen core, 2 frozen core, and 0 frozen core) have been applied to examine the importance of 1s, 2s, and 2p core electrons. With the SCF method two isomers (A and B) were found for HSiO. However, at the CISD level o...

  • the gaoh hgao potential energy hypersurface and the necessity of correlating the 3d electrons
    Journal of Chemical Physics, 1996
    Co-Authors: Claude A Richards, Yukio Yamaguchi, Henry F. Schaefer
    Abstract:

    The ground state potential energy hypersurface of the GaOH–HGaO system has been investigated using high level ab initio molecular electronic structure theory. The geometries and physical properties of two equilibrium structures, one isomerization transition state and one inversion transition state were determined at the self‐consistent field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory with four sets of basis functions. It has been found that freezing the 3d electrons of the Ga atom in the correlation procedures is not appropriate for this system. For the energy difference ΔE (GaOH–HGaO) the freezing of the 3d electrons results in an error of 25 kcal/mol! The dipole moments, harmonic vibrational frequencies, and infrared (IR) intensities are predicted for the four stationary points. At the highest level of theory employed in this study, CCSD(T) ...

  • high level ab initio study on the ground state potential energy hypersurface of the hco coh system
    Journal of Chemical Physics, 1994
    Co-Authors: Yukio Yamaguchi, Claude A Richards, Henry F. Schaefer
    Abstract:

    The ground state potential energy hypersurface of the HCO+–COH+ system has been reinvestigated systematically using high level ab initio electronic structure theory. The geometries and physical properties of the two equilibrium and one isomerization transition state structures were determined at the self‐consistent‐field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory with nine basis sets. First, the optimized geometries of the three stationary points at twenty eight (28) levels of theory were discussed. Second, the characteristics and responses of the molecular orbitals (MOs) with respect to the normal coordinates have been elucidated via energy derivative analysis technique. Third, dipole moments, harmonic vibrational frequencies, and infrared (IR) intensities were described. Finally, the relative energies among the stationary points have been co...

  • striking similarities between elementary silicon and aluminum compounds monobridged dibridged trans bent and vinylidene isomers of aluminum hydride al2h2
    Journal of the American Chemical Society, 1993
    Co-Authors: Zoltan Palagyi, Roger S Grev, Henry F. Schaefer
    Abstract:

    Ab initio quantum mechanical methods five been used to study the singlet potential energy surface of Al 2 H 2 . Optimum geometries and harmonic vibrational frequencies were obtained for four geometrical isomers using the self-consistent-field (SCF), configuration interaction (CI), and coupled cluster (CC) methods. Both correlation methods including single and double excitations (CISD, CCSD) were employed, and all wave functions were determined with both DZP and TZ2P basis sets. Final energy predictions are obtained using large atomic natural orbital basis sets, and including the effects of triple excitations perturbatively using CCSD(T) methods. We found the planar dibridged structure to be the global minimum, as predicted earlier by Baird

Piotr Piecuch - One of the best experts on this subject based on the ideXlab platform.

  • application of the cc p q hierarchy of coupled cluster methods to the beryllium dimer
    Journal of Physical Chemistry A, 2017
    Co-Authors: Ilias Magoulas, Nicholas P Bauman, Jun Shen, Piotr Piecuch
    Abstract:

    The performance of coupled-cluster approaches with higher-than-doubly excited clusters, including the CCSD(T), CCSD(2)T, CR-CC(2,3), CCSD(TQ), and CR-CC(2,4) corrections to CCSD, the active-space CCSDt, CCSDtq, and CCSDTq methods, and the CC(t;3), CC(t,q;3), CC(t,q;3,4), and CC(q;4) corrections to CCSDt, CCSDtq, and CCSDTq resulting from the CC(P;Q) formalism, in reproducing the CCSDT and CCSDTQ potential energy curves and vibrational term values characterizing Be2 in its electronic ground state is assessed. The correlation-consistent aug-cc-pVnZ and aug-cc-pCVnZ (n = T and Q) basis sets are employed. Among the CCSD-based corrections, the completely renormalized CR-CC(2,3) and CR-CC(2,4) approaches perform the best. The CC(t;3), CC(t,q;3), CC(t,q;3,4), and CC(q;4) methods, especially CC(t;3) and CC(q;4), outperform other employed approaches in reproducing the CCSDT and CCSDTQ data. Composite schemes combining the all-electron CCSDT calculations extrapolated to the complete basis set limit with the frozen-...

  • geometries binding energies ionization potentials and electron affinities of metal clusters mgn0 1 n 1 7
    Journal of Physical Chemistry C, 2016
    Co-Authors: Kaining Duanmu, Piotr Piecuch, Jun Shen, Orlando Robertoneto, Francisco B C Machado, Jared A Hansen, Donald G Truhlar
    Abstract:

    Equilibrium geometries, binding energies, adiabatic ionization potentials, and adiabatic electron affinities for neutral and singly charged magnesium clusters, Mgn0, ± 1, n = 1–7, have been computed using 39 exchange-correlation (XC) functionals in Kohn–Sham density functional theory and several coupled-cluster methods with single, double, and triple excitations, including CCSD(T) for all species, CCSD(2)T and CR-CC(2,3) for species with n = 1–3, and CCSDt, CC(t;3), and CCSDT for species with n = 1 and 2. We have used augmented polarized–valence and polarized–core–valence correlation-consistent basis sets. We have found that the geometry and binding energy of the weakly bound Mg2 dimer requires a robust treatment of connected triple excitations, represented in this work by the CR-CC(2,3), CC(t;3), and full CCSDT methods, which are more accurate than the popular quasi-perturbative CCSD(T) approximation, but CCSD(T) is sufficiently accurate to be applied to other Mg clusters. We have also demonstrated that ...

  • geometries binding energies ionization potentials and electron affinities of metal clusters mgn0 1 n 1 7
    Journal of Physical Chemistry C, 2016
    Co-Authors: Kaining Duanmu, Piotr Piecuch, Jun Shen, Orlando Robertoneto, Francisco B C Machado, Jared A Hansen, Donald G Truhlar
    Abstract:

    Equilibrium geometries, binding energies, adiabatic ionization potentials, and adiabatic electron affinities for neutral and singly charged magnesium clusters, Mgn0, ± 1, n = 1–7, have been computed using 39 exchange-correlation (XC) functionals in Kohn–Sham density functional theory and several coupled-cluster methods with single, double, and triple excitations, including CCSD(T) for all species, CCSD(2)T and CR-CC(2,3) for species with n = 1–3, and CCSDt, CC(t;3), and CCSDT for species with n = 1 and 2. We have used augmented polarized–valence and polarized–core–valence correlation-consistent basis sets. We have found that the geometry and binding energy of the weakly bound Mg2 dimer requires a robust treatment of connected triple excitations, represented in this work by the CR-CC(2,3), CC(t;3), and full CCSDT methods, which are more accurate than the popular quasi-perturbative CCSD(T) approximation, but CCSD(T) is sufficiently accurate to be applied to other Mg clusters. We have also demonstrated that ...

  • a comparison of the renormalized and active space coupled cluster methods potential energy curves of bh and f2
    Chemical Physics Letters, 2001
    Co-Authors: Piotr Piecuch
    Abstract:

    Abstract The renormalized noniterative CCSD(T) and CCSD(TQ) methods, which are the examples of the method of moments of coupled-cluster (CC) equations, and the active-space CC approach with internal and semi-internal triexcited clusters (CCSDt) are applied to the potential energy curves of BH and F 2 . It is shown that the renormalized CCSD(T) and CCSD(TQ) methods are practically as effective in removing the failing of the standard noniterative CC approaches at larger internuclear separations as the CCSDt method. The results of the CCSDt and renormalized CCSD(T) and CCSD(TQ) calculations are also compared with those obtained with other perturbative CC approaches that focus on bond breaking.

Robert J Siegel - One of the best experts on this subject based on the ideXlab platform.

  • iatrogenic atrial septal defect after percutaneous mitral valve repair with the mitraclip system
    American Journal of Cardiology, 2017
    Co-Authors: Kentaro Toyama, Florian Rader, Saibal Kar, Shunsuke Kubo, Takahiro Shiota, Toshihiko Nishioka, Robert J Siegel
    Abstract:

    This study examines the incidence of iatrogenic atrial septal defect (iASD) after the MitraClip procedure and its influence on echocardiographic and clinical outcomes. We examined 96 patients who underwent a successful MitraClip procedure and who also had baseline and 1-year postprocedure transthoracic echocardiograms. At 1-year follow-up, iASD were observed in 24% of cases. Compared with the patients without iASD, the patients with iASD had a larger right atrium and greater severity of tricuspid regurgitation (TR) at baseline. After the MitraClip procedure, mitral regurgitation lessened significantly in both groups. Although right atrial area and right ventricular diameters increased significantly in patients with iASD (25.3 ± 8.0 to 28.3 ± 9.5 cm2, 39.7 ± 7.1 to 42.2 ± 8.1 mm, p <0.05 for both comparisons), these variables did not change in patients without iASD. In addition, patients with iASD had worse TR at follow-up. The incidence of stroke was comparable between the 2 groups during 1-year follow-up (4.3% vs 4.1%). However, patients with iASD had a markedly higher re-hospitalization rate for heart failure (26% vs 2.7%, p <0.05). In conclusion, iASD occurred in 24% of patients who underwent the MitraClip therapy and the presence of iASD was associated with right-sided heart enlargement, worse TR, and a higher re-hospitalization rate for heart failure.

Donald G Truhlar - One of the best experts on this subject based on the ideXlab platform.

  • geometries binding energies ionization potentials and electron affinities of metal clusters mgn0 1 n 1 7
    Journal of Physical Chemistry C, 2016
    Co-Authors: Kaining Duanmu, Piotr Piecuch, Jun Shen, Orlando Robertoneto, Francisco B C Machado, Jared A Hansen, Donald G Truhlar
    Abstract:

    Equilibrium geometries, binding energies, adiabatic ionization potentials, and adiabatic electron affinities for neutral and singly charged magnesium clusters, Mgn0, ± 1, n = 1–7, have been computed using 39 exchange-correlation (XC) functionals in Kohn–Sham density functional theory and several coupled-cluster methods with single, double, and triple excitations, including CCSD(T) for all species, CCSD(2)T and CR-CC(2,3) for species with n = 1–3, and CCSDt, CC(t;3), and CCSDT for species with n = 1 and 2. We have used augmented polarized–valence and polarized–core–valence correlation-consistent basis sets. We have found that the geometry and binding energy of the weakly bound Mg2 dimer requires a robust treatment of connected triple excitations, represented in this work by the CR-CC(2,3), CC(t;3), and full CCSDT methods, which are more accurate than the popular quasi-perturbative CCSD(T) approximation, but CCSD(T) is sufficiently accurate to be applied to other Mg clusters. We have also demonstrated that ...

  • geometries binding energies ionization potentials and electron affinities of metal clusters mgn0 1 n 1 7
    Journal of Physical Chemistry C, 2016
    Co-Authors: Kaining Duanmu, Piotr Piecuch, Jun Shen, Orlando Robertoneto, Francisco B C Machado, Jared A Hansen, Donald G Truhlar
    Abstract:

    Equilibrium geometries, binding energies, adiabatic ionization potentials, and adiabatic electron affinities for neutral and singly charged magnesium clusters, Mgn0, ± 1, n = 1–7, have been computed using 39 exchange-correlation (XC) functionals in Kohn–Sham density functional theory and several coupled-cluster methods with single, double, and triple excitations, including CCSD(T) for all species, CCSD(2)T and CR-CC(2,3) for species with n = 1–3, and CCSDt, CC(t;3), and CCSDT for species with n = 1 and 2. We have used augmented polarized–valence and polarized–core–valence correlation-consistent basis sets. We have found that the geometry and binding energy of the weakly bound Mg2 dimer requires a robust treatment of connected triple excitations, represented in this work by the CR-CC(2,3), CC(t;3), and full CCSDT methods, which are more accurate than the popular quasi-perturbative CCSD(T) approximation, but CCSD(T) is sufficiently accurate to be applied to other Mg clusters. We have also demonstrated that ...