33S hyperfine interactions in H2S and SO2 and revision of the sulfur nuclear magnetic shielding scale

2014

Using the Lamb-dip technique, the hyperfine structure in the rotational spectra of H2(33)S and (33)SO2 has been resolved and the corresponding parameters--that is, the sulfur quadrupole-coupling and spin-rotation tensors--were determined. The experimental parameters are in good agreement with results from high-level coupled-cluster calculations, provided that up to quadruple excitations are considered in the cluster operator, sufficiently large basis sets are used, and vibrational corrections are accounted for. The (33)S spin-rotation tensor for H2S has been used to establish a new sulfur nuclear magnetic shielding scale, combining the paramagnetic part of the shielding as obtained from the…

The prediction of molecular equilibrium structures by the standard electronic wave functions

1997

A systematic investigation has been carried out of the accuracy of molecular equilibrium structures of 19 small closed-shell molecules containing first-row atoms as predicted by the following standard electronic ab initio models: Hartree–Fock (HF) theory, Mo/ller–Plesset theory to second, third, and fourth orders (MP2, MP3, and MP4), coupled-cluster singles and doubles (CCSD) theory; CCSD theory with perturbational triples corrections [CCSD(T)], and the configuration-interaction singles and doubles (CISD) model. For all models, calculations were carried out using the correlation-consistent polarized valence double-zeta (cc-pVDZ) basis, the correlation-consistent polarized valence triple-zet…

CCSDT calculations of molecular equilibrium geometries

1997

Abstract CCSDT equilibrium geometries of CO, CH2, F2, HF, H2O and N2 have been calculated using the correlation-consistent cc-pVXZ basis sets. Similar calculations have been performed for SCF, CCSD and CCSD(T). In general, bond lengths decrease when improving the basis set and increase when improving the N-electron treatment. CCSD(T) provides an excellent approximation to CCSDT for bond lengths as the largest difference between CCSDT and CCSD(T) is 0.06 pm. At the CCSDT/cc-pVQZ level, basis set deficiencies, neglect of higher-order excitations, and incomplete treatment of core-correlation all give rise to errors of a few tenths of a pm, but to a large extent, these errors cancel. The CCSDT/…

A comparison of density-functional-theory and coupled-cluster frequency-dependent polarizabilities and hyperpolarizabilities

2005

The frequency-dependent polarizabilities and hyperpolarizabilities of HF, CO, H2O and para-nitroaniline calculated by density-functional theory are compared with accurate coupled-cluster results. Whereas the local-density approximation and the generalized gradient approximation (BLYP) perform very similarly and overestimate polarizabilities and, in particular, the hyperpolarizabilities, hybrid density-functional theory (B3LYP) performs better and produces results similar to those obtained by coupled-cluster singles-and-doubles theory. Comparisons are also made for singlet excitation energies, calculated using linear response theory.

Accurate molecular geometries of the protonated water dimer

2000

The equilibrium geometry of the protonated water dimer, H5O2+, was studied using Moller–Plesset perturbation theory and coupled-cluster theory. Constrained geometry optimizations were carried out for the C2 and Cs symmetric structures within the counterpoise framework and near the limit of a complete basis set. In the constrained optimization, the degrees of freedom of the complex are reduced to an intrafragmental distortion and an interfragmental coordinate, making the procedure tractable for large basis sets and explicitly correlated linear r12 methods. The energy of the stationary point of C2 symmetry was found to be 1.2 kJ mol−1 below the energy of the Cs structure.

Foreword: Prof. Gauss Festschrift

2020

As guest editors, we are excited to present the Molecular Physics Festschrift in honour of Jurgen Gauss, professor of theoretical chemistry at the Johannes Gutenberg-Universitat Mainz, Germany, on ...

A computational study of some electric and magnetic properties of gaseous BF3 and BCl3

2005

We present the results of an extended computational study of the electric and magnetic properties connected to Cotton-Mouton birefringences, on the trifluoro- and trichloroborides in the gas phase. The electric dipole polarizabilities, magnetizabilities, quadrupole moments, and higher-order hypersusceptibilities—expressed as quadratic and cubic frequency-dependent response functions—are computed within Hartree-Fock, density-functional, and coupled-cluster response theories employing singly and doubly augmented correlation-consistent basis sets and London orbitals in the magnetic property calculations. The results, which illustrate the capability of time-dependent density-functional theory f…

The Dalton quantum chemistry program system

2013

Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree-Fock, Kohn-Sham, multiconfigurational self-consistent-field, MOller-Plesset, confi ...

The CC3 model : An iterative coupled cluster approach including connected triples

1997

An alternative derivation of many-body perturbation theory (MBPT) has been given, where a coupled cluster parametrization is used for the wave function and the method of undetermined Lagrange multipliers is applied to set up a variational coupled cluster energy expression. In this variational formulation, the nth-order amplitudes determine the energy to order 2n+1 and the nth-order multipliers determine the energy to order 2n+2. We have developed an iterative approximate coupled cluster singles, doubles, and triples model CC3, where the triples amplitudes are correct through second order and the singles amplitudes are treated without approximations due to the unique role of singles as appro…

Kohn–Sham energy decomposition for molecules in a magnetic field

2018

We study the total molecular electronic energy and its Kohn–Sham components within the framework of magnetic-field density-functional theory (BDFT), an alternative to current-dependent density-functional theory (CDFT) for molecules in the presence of magnetic fields. For a selection of closed-shell dia- and paramagnetic molecules, we investigate the dependence of the total electronic energy and its Kohn–Sham components on the magnetic field. Results obtained from commonly used density-functional approximations are compared with those obtained from Lieb optimizations based on magnetic-field dependent relaxed coupled-cluster singles-and-doubles (CCSD) and second-order Moller–Plesset (MP2) den…

Basis-set completeness profiles in two dimensions

2002

A two-electron basis-set completeness profile is proposed by analogy with the one-electron profile introduced by D. P. Chong (Can J Chem 1995, 73, 79). It is defined as Y(alpha, beta) = sigmam sigman (Galpha(1)Gbeta(2)/(1/r12)/ psim(1)psin(2)) (psim(1)psin(2)/r12/Galpha(1)Gp(2)) and motivated by the expression for the basis-set truncation correction that occurs in the framework of explicitly correlated methods (Galpha is a scanning Gaussian-type orbital of exponent alpha and [psim] is the orthonormalized one-electron basis under study). The two-electron basis-set profiles provide a visual assessment of the suitability of basis sets to describe electron-correlation effects. Furthermore, they…

Coupled-cluster singles, doubles and triples (CCSDT) calculations of atomization energies

2000

Atomization energies have been calculated for CO, H2O, F-2, HF, N-2 and CH2 (the (1)A(1) state) using the coupled-duster singles, doubles and triples (CCSDT) model as well as the coupled-cluster singles and doubles model with a perturbative correction for triples [CCSD(T)]. TheCCSD(T) model provides an excellent approximation to the CCSDT model; at the cc-pV5Z basis set level, the CCSDT valence triples contribution is underestimated by 9.1% (0.8 kJ/mol) for CH, and overestimated for the remaining molecules by as little as 4.3%(1.3 kJ/mol) for F-2,and as much as 8.4% (3.0 kJ/mol) for N-2. At the CCSDT level, the agreement with experiment is not improved, suggesting that some cancellation of …

Large-scale calculations of excitation energies in coupled cluster theory: The singlet excited states of benzene

1996

Algorithms for calculating singlet excitation energies in the coupled cluster singles and doubles (CCSD) model are discussed and an implementation of an atomic-integral direct algorithm is presented. Each excitation energy is calculated at a cost comparable to that of the CCSD ground-state energy. Singlet excitation energies are calculated for benzene using up to 432 basis functions. Basis-set effects of the order of 0.2 eV are observed when the basis is increased from augmented polarized valence double-zeta (aug-cc-pVDZ) to augmented polarized valence triple-zeta (aug-cc-pVTZ) quality. The correlation problem is examined by performing calculations in the hierarchy of coupled cluster models…

Erratum: “GW quasiparticle energies of atoms in strong magnetic fields” [J. Chem. Phys. 150, 214112 (2019)]

2019

Coupled-cluster theory for atoms and molecules in strong magnetic fields

2015

An implementation of coupled-cluster (CC) theory to treat atoms and molecules in finite magnetic fields is presented. The main challenges for the implementation stem from the magnetic-field dependence in the Hamiltonian, or, more precisely, the appearance of the angular momentum operator, due to which the wave function becomes complex and which introduces a gauge-origin dependence. For this reason, an implementation of a complex CC code is required together with the use of gauge-including atomic orbitals to ensure gauge-origin independence. Results of coupled-cluster singles-doubles-perturbative-triples (CCSD(T)) calculations are presented for atoms and molecules with a focus on the depende…

GW quasiparticle energies of atoms in strong magnetic fields

2019

Quasiparticle energies of the atoms H–Ne have been computed in the GW approximation in the presence of strong magnetic fields with field strengths varying from 0 to 0.25 atomic units (0.25 B 0 =0.25 ℏe −1 a −2 0 ≈58 763 0.25 B0=0.25 ℏe−1a0−2≈58 763 T). The GW quasiparticle energies are compared with equation-of-motion ionization-potential (EOM-IP) coupled-cluster singles-and-doubles (CCSD) calculations of the first ionization energies. The best results are obtained with the evGW@PBE0 method, which agrees with the EOM-IP-CCSD model to within about 0.20 eV. Ionization potentials have been calculated for all atoms in the series, representing the first systematic study of ionization potentials …

The accuracy of molecular dipole moments in standard electronic structure calculations

2000

Abstract A systematic investigation has been carried out of the accuracy of calculated molecular equilibrium dipole moments of 11 polar closed-shell molecules, using the HF, MP2, CCSD and CCSD(T) models and correlation-consistent basis sets. Augmented basis sets are important for improving the basis-set convergence, but the quality of the results depends more on the correlation treatment than on the cardinal number of the basis set. Augmented triple-zeta basis sets are sufficient for most calculations. The mean absolute error of the HF calculations is 0.16 D, which is reduced at the MP2 and CCSD levels to 0.048 and 0.025 D, respectively. The CCSD(T) errors are small – typically

Molecular equilibrium structures from experimental rotational constants and calculated vibration–rotation interaction constants

2002

A detailed study is carried out of the accuracy of molecular equilibrium geometries obtained from least-squares fits involving experimental rotational constants B(0) and sums of ab initio vibration-rotation interaction constants alpha(r)(B). The vibration-rotation interaction constants have been calculated for 18 single-configuration dominated molecules containing hydrogen and first-row atoms at various standard levels of ab initio theory. Comparisons with the experimental data and tests for the internal consistency of the calculations show that the equilibrium structures generated using Hartree-Fock vibration-rotation interaction constants have an accuracy similar to that obtained by a dir…

The integral‐direct coupled cluster singles and doubles model

1996

An efficient and highly vectorized implementation of the coupled cluster singles and doubles (CCSD) model using a direct atomic integral technique is presented. The minimal number of n6processes has been implemented for the most time consuming terms and point group symmetry is used to further reduce operation counts and memory requirements. The significantly increased application range of the CCSD method is illustrated with sample calculations on several systems with more than 500 basis functions. Furthermore, we present the basic trends of an open ended algorithm and discuss the use of integral prescreening. © 1996 American Institute of Physics.