Archivio della ricerca di Triestehttps://arts.units.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Thu, 29 Oct 2020 17:53:55 GMT2020-10-29T17:53:55Z101371Implementation of the Incremental Scheme for One-Electron First-Order Properties in Coupled-Cluster Theoryhttp://hdl.handle.net/11368/2283027Titolo: Implementation of the Incremental Scheme for One-Electron First-Order Properties in Coupled-Cluster Theory
Abstract: A fully automated parallelized implementation of the incremental scheme for coupled-cluster
singles-and-doubles (CCSD) energies has been extended to treat molecular (unrelaxed) first-order
one-electron properties such as the electric dipole and quadrupole moments. The convergence and
accuracy of the incremental approach for the dipole and quadrupole moments have been studied for
a variety of chemically interesting systems. It is found that the electric dipole moment can be
obtained to within 5% and 0.5% accuracy with respect to the exact CCSD value at the third and
fourth orders of the expansion, respectively. Furthermore, we find that the incremental expansion of
the quadrupole moment converges to the exact result with increasing order of the expansion: the
convergence of nonaromatic compounds is fast with errors less than 16 mau and less than 1 mau at
third and fourth orders, respectively (1 mau=10E-3 e a0^2); the aromatic compounds converge slowly
with maximum absolute deviations of 174 and 72 mau at third and fourth orders, respectively
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/11368/22830272009-01-01T00:00:00ZGauge-origin independent magneto-optical activity within coupled-cluster response theoryhttp://hdl.handle.net/11368/2626036Titolo: Gauge-origin independent magneto-optical activity within coupled-cluster response theory
Abstract: We present a gauge-origin independent formulation of the Faraday B term of magnetic circular dichroism and of the Verdet constant of magneto-optical rotation, in terms of first derivatives with respect to the magnetic field strength of gauge invariant coupled cluster response functionals [1]. Gauge invariance is ensured by the derivative formulation in connection with the use of a magnetic field dependent basis of atomic orbitals, the so-called London orbitals. To our knowledge this represent the first application of London atomic orbitals to the calculation of frequency dependent quadratic response properties. The approach can easily be extended to other wavefunction models, and to any other frequency dependent property which can be formulated as total derivative of a (frequency-dependent) functional with respect to the field strengths of a static magnetic perturbation. In other words, any properties for which the frequency dependence is not associated with the magnetic field. This is for example the case for the hypermagnetizabilities in the Cotton-Moutton effect. The implementation of the derived equations is currently undertaken for a CCSD wavefunction on a local version of the Dalton program.
[1] S. Coriani, C. Hättig, P. Jørgensen, T. Helgaker
Fri, 01 Jan 1999 00:00:00 GMThttp://hdl.handle.net/11368/26260361999-01-01T00:00:00ZDensity-matrix based formulation of KS response theory with applications to linear and non-linear spectroscopieshttp://hdl.handle.net/11368/2623844Titolo: Density-matrix based formulation of KS response theory with applications to linear and non-linear spectroscopies
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/11368/26238442010-01-01T00:00:00ZCoupled cluster methods for x-ray spectroscopy: the damped linear response functionhttp://hdl.handle.net/11368/2623838Titolo: Coupled cluster methods for x-ray spectroscopy: the damped linear response function
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11368/26238382012-01-01T00:00:00ZOptical rotation calculation of a highly flexible molecule: the case of paraconic acidhttp://hdl.handle.net/11368/1699356Titolo: Optical rotation calculation of a highly flexible molecule: the case of paraconic acid
Abstract: The absolute configuration of (S)-(-)-paraconic acid is correctly assigned on the basis of ab initio calculations of the specific optical rotation (OR) at the sodium D line, carried out both in vacuum and in methanol. Density functional theory (DFT) and Møller-Plesset second-order perturbation theory (MP2) are used to determine the most stable conformational structures, whose OR values are then calculated using DFT linear response theory and London atomic orbitals. The total OR is obtained by averaging these values using the population fractions determined from Boltzmann’s statistics. The total OR of the MP2 structures has the correct sign both in vacuum and in solution, whereas only the solvent-relaxed DFT structures correctly reproduce the experimental sign. The strong solvent effect on the total OR is shown to arise primarily due to the variations in the relative energies of the various conformations.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/11368/16993562005-01-01T00:00:00ZModeling the molecular response to electromagnetic fields: old and new spectroscopies and “exotic” effectshttp://hdl.handle.net/11368/2807140Titolo: Modeling the molecular response to electromagnetic fields: old and new spectroscopies and “exotic” effects
Abstract: Response theory constitutes a powerful and versatile theoretical framework for determining molecular properties and spectra by probing the response to weak (external or internal) electromagnetic fields. It provides efficient computational formulas for both linear and nonlinear response properties, thus describing a plethora of optical effects. Rooted on recent theoretical developments based within the coupled-cluster ansatz and density functional theory, in particular the so-called “damped” formulation of response theory, aka complex polarization propagator, we present results for both “traditional” and new “perspective” spectroscopies related to the absorption of light by the sample in presence external or internal magnetic fields, and in the highly energetic x-ray frequency region.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11368/28071402014-01-01T00:00:00ZVariational response-function formulation of vibrational circular dichroismhttp://hdl.handle.net/11368/2620644Titolo: Variational response-function formulation of vibrational circular dichroism
Abstract: An alternative formulation of the atomic axial tensor (AAT) of vibrational circular dichroism as the frequency derivative at zero frequency of a linear response function for operators referencing a nuclear displacement and a magnetic field is presented [1]. When used in the density matrix-based quasienergy derivative Lagrangian approach of Thorvaldsen et al.[2], this allows to express the AAT in a form where the need to solve response equations for the nuclear displacements is removed, significantly reducing the computation cost compared to existing formulations . The formalism also straightforwardly accounts for all contributions arising from the use of perturbation dependent basis sets.
It is also expected to pave the way for gauge-origin independent implementations of VCD within non-variational wave-function theories.
References
[1] S. Coriani , A. J. Thorvaldsen, K. Kristensen and Poul Jørgensen,
Phys. Chem. Chem. Phys.13 4224-4229 (2011)
[2] A. Thorvaldsen, K. Ruud, K. Kristensen, P. Jørgensen and
S. Coriani, J. Chem. Phys. 129 214108 (2008).
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11368/26206442012-01-01T00:00:00ZSpin flipping in ring-coupled-cluster-doubles theoryhttp://hdl.handle.net/11368/2336245Titolo: Spin flipping in ring-coupled-cluster-doubles theory
Abstract: We report a critical analysis and comparison of a variety of random-phase-approximation (RPA) based
approaches to determine the electronic ground-state energy. Interrelations between RPA variants are
examined by numerical example with particular attention paid to the role of spin-flipped excitations
and the behaviour of the adiabatic-connection integrands where appropriate. In general, it is found that
RPA variants that include Hartree–Fock exchange contributions are unsuitable as generally applicable
methods for the determination of correlation energies. Of the remaining methods only the direct RPA
and RPA with second-order screened exchange are recommended for general use.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/11368/23362452011-01-01T00:00:00ZThe Dalton quantum chemistry program systemhttp://hdl.handle.net/11368/2769542Titolo: The Dalton quantum chemistry program system
Abstract: 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, Møller–Plesset, configuration‐interaction, and coupled‐cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic‐structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge‐origin‐invariant manner. Frequency‐dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one‐, two‐, and three‐photon processes. Environmental effects may be included using various dielectric‐medium and quantum‐mechanics/molecular‐mechanics models. Large molecules may be studied using linear‐scaling and massively parallel algorithms. Dalton is distributed at no cost from http://www.daltonprogram.org for a number of UNIX platforms
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11368/27695422014-01-01T00:00:00ZDalton, a molecular electronic structure program,
Release Dalton2011http://hdl.handle.net/11368/2620643Titolo: Dalton, a molecular electronic structure program,
Release Dalton2011
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/11368/26206432011-01-01T00:00:00Z