Potential functions of the ground and low excited states of Al 2 are calculated by the relativist... more Potential functions of the ground and low excited states of Al 2 are calculated by the relativistic Fock-space coupled cluster method in the framework of the projected Dirac-Coulomb Hamiltonian. A moderate-size basis [16s11p3d3f/6s6p3d2f ] is used. 3 Π u is confirmed as the ground state of the system. Its spin orbit splittings are reproduced well, with the Λ = 1, 2 states lying 32.5 and 66.1 cm −1 , respectively, above the Λ = 0 minimum (experimental values are 30.4 and 63.4 cm −1 ). The bond is somewhat too weak, with D e 0.14 eV below experiment, R e too high by 0.08Å, and ω e 21 cm −1 too low. It is speculated that the better agreement obtained in earlier calculations may be due to neglect of basis set superposition errors. The description of bonding in the molecule may be improved by the use of a better basis and the inclusion of more correlation by the intermediate Hamiltonian coupled cluster method, which makes it possible to handle larger P spaces and extend the potential functions to the whole range of internuclear separations.
... J. Quantum Chem. 52 (1994) 1369. [12] J, Meyer, WD Sepp, B. Fricke and A. Rosen, Comp. Phys. ... more ... J. Quantum Chem. 52 (1994) 1369. [12] J, Meyer, WD Sepp, B. Fricke and A. Rosen, Comp. Phys. Commun. ... 52 (1994), p. 1369. Full Text via CrossRef. [12]. J. Meyer, W.-D. Sepp, B. Fricke and A. Rosen. Comp. Phys. Commun. 21 (1989), p. 2559. [13]. JG Snijders. ...
The potential energy curve for the ground-state of radium dimer (Ra2) is provided by means of ato... more The potential energy curve for the ground-state of radium dimer (Ra2) is provided by means of atomic and molecular relativistic coupled cluster calculations. The short-range part of this curve is defined by an equilibrium bond length of 5.324 Å, a dissociation energy of 897 cm(-1), and a harmonic vibrational frequency of 20.5 cm(-1). The asymptotic behavior at large interatomic distances is characterized by the van der Waals coefficients C6 = 5.090 × 10(3), C8 = 6.978 × 10(5), and C10 = 8.786 × 10(7) atomic units. The two regions are matched in an analytical potential to provide a convenient representation for use in further calculations, for instance, to model cold collisions between radium atoms. This might become relevant in future experiments on ultracold, optically trapped, radioactive radium atoms that are used to search for a permanent electric dipole moment.
The efficacy of the frozen density embedding (FDE) approach to the simulation of solvent effects ... more The efficacy of the frozen density embedding (FDE) approach to the simulation of solvent effects is examined for two key chiroptical properties-specific rotation and circular dichroism spectra. In particular, we have investigated the performance of a wave function-theory-in-density-functional-theory (WFT-in-DFT) FDE approach for computing such properties for the small, rigid chiral compound (P)-dimethylallene interacting with up to three water molecules. Although the solvent potential is obtained through DFT, the optical response is computed using coupled cluster linear response theory for mixed electric and magnetic field perturbations. We find that the FDE potential generally yields too small a shift from the isolated molecule as compared to that introduced by the explicit solvent. In one case, the FDE potential fails to reproduce a change in sign of the ORD in which the solute interacts with two solvent molecules. The source of these errors is due primarily to the lack of solvent response to the external field and is analyzed in terms of solvent-solute charge transfer excitations.
Cationic cobalt clusters complexed with water Co_n+H2O (n=4-20) are produced through laser ablati... more Cationic cobalt clusters complexed with water Co_n+H2O (n=4-20) are produced through laser ablation and investigated via Infrared Multiple Photon Dissociation (IR-MPD) spectroscopy in the 200-1700 cm-1 spectral range. All spectra exhibit a resonance close to the 1595 cm-1 frequency of the free water bending vibration, indicating that the water molecule remains intact upon adsorption. For n = 4, the frequency of this band is blue shifted, but it gradually converges on the free water value with increasing cluster size. In the lower frequency range (200-650 cm-1) the spectra contain several bands which show a very regular frequency evolution, suggesting that the exact cluster geometry has little effect on the water-surface interaction. Density functional theory (DFT) calculations are carried out at the OPBE/TZVP level for three representative sizes (n = 6, 9, 13) and indicate that the vibrations responsible for the resonances correspond to bending and torsional modes between the cluste...
The nuclear quadrupole moment of 115 In has been determined by combining the experimental nuclear... more The nuclear quadrupole moment of 115 In has been determined by combining the experimental nuclear quadrupole coupling constants and electric field gradients, calculated at the four-component CCSD͑T͒ level of theory, of four indium halides. Our recommended value for the nuclear quadrupole moment of 115 In is 770͑8͒ millibarn. A basis set study at the Dirac-Hartree-Fock level shows a slow convergence of the electric field gradient with respect to higher angular momentum functions.
A simple point-charge model is used to correct molecular four-component Dirac-Coulomb calculation... more A simple point-charge model is used to correct molecular four-component Dirac-Coulomb calculations which neglect two-electron integrals over the small components of the wave function. The calculated valence properties show no degeneration relative to the full calculation, while a speed-up factor of 3 is obtained.
Two recently proposed formally exact theories for the relativistic calculation of nuclear shieldi... more Two recently proposed formally exact theories for the relativistic calculation of nuclear shielding tensors are numerically evaluated for the xenon atom and the hydrogen fluoride and hydrogen iodide molecules. Both theories are shown to yield significantly different shieldings and partitionings into diamagnetic and paramagnetic contributions. A short analysis is given and directions for further research are indicated.
. The spectroscopic parameters of the ground state of thallium hydride are obtained using the f... more . The spectroscopic parameters of the ground state of thallium hydride are obtained using the four-component relativistic Dirac–Coulomb–Gaunt–coupled-cluster wave function with single and double excitations and an estimated triples correction method. Core correlation effects make the bond weaker but have little effect on the bond length. Inclusion of the distance dependence of the Gaunt part of the two-electron Breit interaction
Recently we reported a combined QM/MM approach to estimate condensed-phase values of atomic polar... more Recently we reported a combined QM/MM approach to estimate condensed-phase values of atomic polarizabilities for use in (bio)molecular simulation. The setup relies on a MM treatment of the solvent when determining atomic polarizabilities to describe the response of a QM described solute to its external electric field. In this work, we study the effect of using alternative descriptions of the solvent molecules when evaluating atomic polarizabilities of a methanol solute. In a first step, we show that solute polarizabilities are not significantly affected upon substantially increasing the MM dipole moments towards values that are typically reported in literature for water solvent molecules. Subsequently, solute polarization is evaluated in the presence of a QM described solvent (using the frozen-density embedding method). In the latter case, lower oxygen polarizabilities were obtained than when using MM point charges to describe the solvent, due to introduction of Pauli-repulsion effects.
A perspective on the use of the relativistic Dirac equation in quantum chemistry is given. It is ... more A perspective on the use of the relativistic Dirac equation in quantum chemistry is given. It is demonstrated that many of the computational problems that plague the current implementations of the different electronic structure methods can be overcome by utilizing the locality of the small component wave function and density. Possible applications of such new and more efficient formulations are discussed.
The nuclear quadrupole moment of 115In has been determined by combining the experimental nuclear ... more The nuclear quadrupole moment of 115In has been determined by combining the experimental nuclear quadrupole coupling constants and electric field gradients, calculated at the four-component CCSD(T) level of theory, of four indium halides. Our recommended value for the nuclear quadrupole moment of 115In is 770(8) millibarn. A basis set study at the Dirac-Hartree-Fock level shows a slow convergence of the
Page 1. Relativistic and Electron Correlation Effects for Molecules of Heavy Elements: Ab Initio ... more Page 1. Relativistic and Electron Correlation Effects for Molecules of Heavy Elements: Ab Initio Fully Relativistic Coupled-Cluster Calculations for PbH4 GULZARI L. MALLI,1 MARTIN SIEGERT,2 DAVID P. TURNER3 1Department ...
A study is presented comparing molecular structures using plane wave pseudopotential and conventi... more A study is presented comparing molecular structures using plane wave pseudopotential and conventional Gaussian basis density functional methods. The relative accuracy of the two methods is discussed for a range of small molecules. The results show that the plane wave method can reproduce the accuracy of large Gaussian basis calculations for non-periodic systems with a competitive compute time.
Potential functions of the ground and low excited states of Al 2 are calculated by the relativist... more Potential functions of the ground and low excited states of Al 2 are calculated by the relativistic Fock-space coupled cluster method in the framework of the projected Dirac-Coulomb Hamiltonian. A moderate-size basis [16s11p3d3f/6s6p3d2f ] is used. 3 Π u is confirmed as the ground state of the system. Its spin orbit splittings are reproduced well, with the Λ = 1, 2 states lying 32.5 and 66.1 cm −1 , respectively, above the Λ = 0 minimum (experimental values are 30.4 and 63.4 cm −1 ). The bond is somewhat too weak, with D e 0.14 eV below experiment, R e too high by 0.08Å, and ω e 21 cm −1 too low. It is speculated that the better agreement obtained in earlier calculations may be due to neglect of basis set superposition errors. The description of bonding in the molecule may be improved by the use of a better basis and the inclusion of more correlation by the intermediate Hamiltonian coupled cluster method, which makes it possible to handle larger P spaces and extend the potential functions to the whole range of internuclear separations.
... J. Quantum Chem. 52 (1994) 1369. [12] J, Meyer, WD Sepp, B. Fricke and A. Rosen, Comp. Phys. ... more ... J. Quantum Chem. 52 (1994) 1369. [12] J, Meyer, WD Sepp, B. Fricke and A. Rosen, Comp. Phys. Commun. ... 52 (1994), p. 1369. Full Text via CrossRef. [12]. J. Meyer, W.-D. Sepp, B. Fricke and A. Rosen. Comp. Phys. Commun. 21 (1989), p. 2559. [13]. JG Snijders. ...
The potential energy curve for the ground-state of radium dimer (Ra2) is provided by means of ato... more The potential energy curve for the ground-state of radium dimer (Ra2) is provided by means of atomic and molecular relativistic coupled cluster calculations. The short-range part of this curve is defined by an equilibrium bond length of 5.324 Å, a dissociation energy of 897 cm(-1), and a harmonic vibrational frequency of 20.5 cm(-1). The asymptotic behavior at large interatomic distances is characterized by the van der Waals coefficients C6 = 5.090 × 10(3), C8 = 6.978 × 10(5), and C10 = 8.786 × 10(7) atomic units. The two regions are matched in an analytical potential to provide a convenient representation for use in further calculations, for instance, to model cold collisions between radium atoms. This might become relevant in future experiments on ultracold, optically trapped, radioactive radium atoms that are used to search for a permanent electric dipole moment.
The efficacy of the frozen density embedding (FDE) approach to the simulation of solvent effects ... more The efficacy of the frozen density embedding (FDE) approach to the simulation of solvent effects is examined for two key chiroptical properties-specific rotation and circular dichroism spectra. In particular, we have investigated the performance of a wave function-theory-in-density-functional-theory (WFT-in-DFT) FDE approach for computing such properties for the small, rigid chiral compound (P)-dimethylallene interacting with up to three water molecules. Although the solvent potential is obtained through DFT, the optical response is computed using coupled cluster linear response theory for mixed electric and magnetic field perturbations. We find that the FDE potential generally yields too small a shift from the isolated molecule as compared to that introduced by the explicit solvent. In one case, the FDE potential fails to reproduce a change in sign of the ORD in which the solute interacts with two solvent molecules. The source of these errors is due primarily to the lack of solvent response to the external field and is analyzed in terms of solvent-solute charge transfer excitations.
Cationic cobalt clusters complexed with water Co_n+H2O (n=4-20) are produced through laser ablati... more Cationic cobalt clusters complexed with water Co_n+H2O (n=4-20) are produced through laser ablation and investigated via Infrared Multiple Photon Dissociation (IR-MPD) spectroscopy in the 200-1700 cm-1 spectral range. All spectra exhibit a resonance close to the 1595 cm-1 frequency of the free water bending vibration, indicating that the water molecule remains intact upon adsorption. For n = 4, the frequency of this band is blue shifted, but it gradually converges on the free water value with increasing cluster size. In the lower frequency range (200-650 cm-1) the spectra contain several bands which show a very regular frequency evolution, suggesting that the exact cluster geometry has little effect on the water-surface interaction. Density functional theory (DFT) calculations are carried out at the OPBE/TZVP level for three representative sizes (n = 6, 9, 13) and indicate that the vibrations responsible for the resonances correspond to bending and torsional modes between the cluste...
The nuclear quadrupole moment of 115 In has been determined by combining the experimental nuclear... more The nuclear quadrupole moment of 115 In has been determined by combining the experimental nuclear quadrupole coupling constants and electric field gradients, calculated at the four-component CCSD͑T͒ level of theory, of four indium halides. Our recommended value for the nuclear quadrupole moment of 115 In is 770͑8͒ millibarn. A basis set study at the Dirac-Hartree-Fock level shows a slow convergence of the electric field gradient with respect to higher angular momentum functions.
A simple point-charge model is used to correct molecular four-component Dirac-Coulomb calculation... more A simple point-charge model is used to correct molecular four-component Dirac-Coulomb calculations which neglect two-electron integrals over the small components of the wave function. The calculated valence properties show no degeneration relative to the full calculation, while a speed-up factor of 3 is obtained.
Two recently proposed formally exact theories for the relativistic calculation of nuclear shieldi... more Two recently proposed formally exact theories for the relativistic calculation of nuclear shielding tensors are numerically evaluated for the xenon atom and the hydrogen fluoride and hydrogen iodide molecules. Both theories are shown to yield significantly different shieldings and partitionings into diamagnetic and paramagnetic contributions. A short analysis is given and directions for further research are indicated.
. The spectroscopic parameters of the ground state of thallium hydride are obtained using the f... more . The spectroscopic parameters of the ground state of thallium hydride are obtained using the four-component relativistic Dirac–Coulomb–Gaunt–coupled-cluster wave function with single and double excitations and an estimated triples correction method. Core correlation effects make the bond weaker but have little effect on the bond length. Inclusion of the distance dependence of the Gaunt part of the two-electron Breit interaction
Recently we reported a combined QM/MM approach to estimate condensed-phase values of atomic polar... more Recently we reported a combined QM/MM approach to estimate condensed-phase values of atomic polarizabilities for use in (bio)molecular simulation. The setup relies on a MM treatment of the solvent when determining atomic polarizabilities to describe the response of a QM described solute to its external electric field. In this work, we study the effect of using alternative descriptions of the solvent molecules when evaluating atomic polarizabilities of a methanol solute. In a first step, we show that solute polarizabilities are not significantly affected upon substantially increasing the MM dipole moments towards values that are typically reported in literature for water solvent molecules. Subsequently, solute polarization is evaluated in the presence of a QM described solvent (using the frozen-density embedding method). In the latter case, lower oxygen polarizabilities were obtained than when using MM point charges to describe the solvent, due to introduction of Pauli-repulsion effects.
A perspective on the use of the relativistic Dirac equation in quantum chemistry is given. It is ... more A perspective on the use of the relativistic Dirac equation in quantum chemistry is given. It is demonstrated that many of the computational problems that plague the current implementations of the different electronic structure methods can be overcome by utilizing the locality of the small component wave function and density. Possible applications of such new and more efficient formulations are discussed.
The nuclear quadrupole moment of 115In has been determined by combining the experimental nuclear ... more The nuclear quadrupole moment of 115In has been determined by combining the experimental nuclear quadrupole coupling constants and electric field gradients, calculated at the four-component CCSD(T) level of theory, of four indium halides. Our recommended value for the nuclear quadrupole moment of 115In is 770(8) millibarn. A basis set study at the Dirac-Hartree-Fock level shows a slow convergence of the
Page 1. Relativistic and Electron Correlation Effects for Molecules of Heavy Elements: Ab Initio ... more Page 1. Relativistic and Electron Correlation Effects for Molecules of Heavy Elements: Ab Initio Fully Relativistic Coupled-Cluster Calculations for PbH4 GULZARI L. MALLI,1 MARTIN SIEGERT,2 DAVID P. TURNER3 1Department ...
A study is presented comparing molecular structures using plane wave pseudopotential and conventi... more A study is presented comparing molecular structures using plane wave pseudopotential and conventional Gaussian basis density functional methods. The relative accuracy of the two methods is discussed for a range of small molecules. The results show that the plane wave method can reproduce the accuracy of large Gaussian basis calculations for non-periodic systems with a competitive compute time.
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