| 1. |
- Aidas, Kestutis, et al.
(author)
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Gauge-origin independent magnetizabilities from hybrid quantum mechanics/molecular mechanics models: Theory and applications to liquid water
- 2007
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In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 442:4-6, s. 322-328
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Journal article (peer-reviewed)abstract
- The theory of a hybrid quantum mechanics/molecular mechanics (QM/MM) approach for gauge-origin independent calculations of the molecular magnetizability using Hartree-Fock or Density Functional Theory is presented. The method is applied to liquid water using configurations generated from classical Molecular Dynamics simulation to calculate the statistical averaged magnetizability. Based on a comparison with experimental data, treating only one water molecule quantum mechanically appears to be insufficient, while a quantum mechanical treatment of also the first solvation shell leads to good agreement between theory and experiment. This indicates that the gas-to-liquid phase shift for the molecular magnetizability is to a large extent of non-electrostatic nature. (c) 2007 Elsevier B.V. All rights reserved.
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| 2. |
- Aidas, Kestutis, et al.
(author)
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Solvent effects on NMR isotropic shielding constants. A comparison between explicit polarizable discrete and continuum approaches
- 2007
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In: The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory. - : American Chemical Society (ACS). - 1520-5215. ; 111:20, s. 4199-4210
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Journal article (peer-reviewed)abstract
- The gas-to-aqueous solution shifts of the O-17 and C-13 NMR isotropic shielding constants for the carbonyl chromophore in formaldehyde and acetone are investigated. For the condensed-phase problem, we use the hybrid density functional theory/molecular mechanics approach in combination with a statistical averaging over an appropriate number of solute-solvent configurations extracted from classical molecular dynamics simulations. The PBE0 exchange-correlation functional and the 6-311++G(2d,2p) basis set are used for the calculation of the shielding constants. London atomic orbitals are employed to ensure gauge-origin independent results. The effects of the bulk solvent molecules are found to be crucial in order to calculate accurate solvation shifts of the shielding constants. Very good agreement between the computed and experimental solvation shifts is obtained for the shielding constants of acetone when a polarizable water potential is used. Supermolecular results based on geometry-optimized molecular structures are presented. We also compare the results obtained with the polarizable continuum model to the results obtained using explicit MM molecules to model the bulk solvent effect.
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| 3. |
- Ferrighi, Lara, et al.
(author)
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Density-functional-theory study of the electric-field-induced second harmonic generation (EFISHG) of push-pull phenylpolyenes in solution
- 2006
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In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 425:4-6, s. 5593-5603
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Journal article (peer-reviewed)abstract
- Density-functional theory and the polarizable continuum model have been used to calculate the electric-field-induced second harmonic generation of a series of push-pull phenylpolyenes in chloroform solution. The calculations have been performed using both the Becke 3-parameter Lee-Yang-Parr functional and the recently developed Coulomb-attenuated method functional. Solvation has been investigated by examining the effects of the reaction field, non-equilibrium solvation, geometry relaxation, and cavity field. The inclusion of solvent effects leads to significantly better agreement with experimental observations.
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| 4. |
- Jiemchooroj, Auayporn, 1978-
(author)
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Long-range intermolecular dispersion forces and circular dichroism spectra from first-principles calculations
- 2007
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Doctoral thesis (other academic/artistic)abstract
- This work presents first-principles calculations of long-range intermolecular dispersion energies between two atoms or molecules and of electronic circular dichroism spectra of chiral molecules. The former is expressed in terms of the C6 dipole-dipole dispersion coefficients Δε, and the latter is given in terms of the extinction coefficient. In a series of publications, the complex linear polarization propagator method has been shown to be a powerful tool to provide accurate ab initio and first-principles density functional theory results. This was the case not only for the C6 dispersion coefficients but also for the electronic circular dichroism at an arbitrary wavelength ranging from the optical to the X-ray regions of the spectrum. The selected samples for the investigation of dispersion interactions in the electronic ground state are the noble gases, n-alkanes, polyacenes, azabenzenes, alkali-metal clusters, and C60. It is found that the values of C6 for the sodium-cluster-to-fullerene interactions are well within the error bars of the experiment. The proposed method can also be used to determine dispersion energies for species in their respective excited electronic states. The C6 dispersion coefficients for the first π → π* excited state of the azabenzene molecules have been obtained with the adopted method in the multiconfiguration self-consistent field approximation. The dispersion energy of the π → π* excited state is smaller than that of the ground state. It is found that the characteristic frequencies ω1 defined in the London approximation of n-alkanes vary in a narrow range which makes it possible to construct a simple structure-to-property relationship based on the number of π-bonds for the dispersion interaction in these saturated compounds. However, this simple approach is not applicable to the interactions of the π-conjugated systems since, depending on the systems, their characteristic frequencies ω1 can vary greatly. In addition, an accomplishment of calculations of the electronic circular dichroism spectra in the near-edge X-ray absorption has been demonstrated.
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| 5. |
- Kongsted, Jacob, et al.
(author)
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Solvent effects on zero-point vibrational corrections to optical rotations and nuclear magnetic resonance shielding constants
- 2008
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In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 451:4-6, s. 226-232
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Journal article (peer-reviewed)abstract
- We present a study of solvent effects on the zero-point vibrational corrections (ZPVC) to optical rotations and nuclear magnetic resonance shielding constants of solvated molecules. The model used to calculate vibrational corrections rely on an expansion of the potential and property surfaces around an effective molecular geometry and includes both harmonic and anharmonic correction. Numerical examples are presented for (S)-propylene oxide in various solvents as well as for acetone and the three diazene molecule. We find that solvent effects on the ZPVCs may be significant and in some cases crucial to accurately predict solvent shifts on molecular properties.
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| 6. |
- Norman, Patrick, et al.
(author)
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Microscopic theory of nonlinear optics
- 2006
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In: Nonlinear optical properties of matter. - : Springer. - 9781402048500 ; , s. 1-49
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Book chapter (peer-reviewed)
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| 7. |
- Pedersen, Thomas, et al.
(author)
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On the importance of vibrational contributions to small-angle optical rotation: Fluoro-oxirane in gas phase and solution.
- 2009
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130:3
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Journal article (peer-reviewed)abstract
- The specific optical rotation of (S)-fluoro-oxirane in gas phase and solution is predicted using time-dependent density functional theory (B3LYP functional) and coupled cluster linear response theory. Upon vibrational averaging, the coupled cluster singles and doubles model predicts the gas phase specific optical rotation to be 8.1 degrees (dm g/cm(3))(-1) at 355 nm at room temperature. This is an order of magnitude smaller than the B3LYP result of 68.4 degrees (dm g/cm(3))(-1). The main source of this discrepancy is the electronic contribution at the equilibrium geometry. The effects of cyclohexane and acetonitrile solvents are calculated for both the electronic and vibrational contributions with the B3LYP functional. The specific optical rotation is estimated to change significantly depending on the polarity of the solvent, increasing in cyclohexane and decreasing in acetonitrile.
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| 8. |
- Rinkevicius, Zilvinas, et al.
(author)
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Degenerate perturbation theory for electronic g tensors : leading-order relativistic effects
- 2008
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In: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 4:11, s. 1810-1828
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Journal article (peer-reviewed)abstract
- A new approach for the evaluation of the leading-order relativistic corrections to the electronic g tensors of molecules with a doublet ground state is presented. The methodology is based on degenerate perturbation theory and includes all relevant contributions to the g tensor shift up to order theta(alpha(4)) originating from the one-electron part of the Breit-Pauli Hamiltonian-that is, it allows for the treatment of scalar relativistic, spin-orbit, and mixed corrections to the spin and orbital Zeeman effects. This approach has been implemented in the framework of spin-restricted density functional theory and is in the present paper, as a first illustration of the theory, applied to study relativistic effects on electronic g tensors of dihalogen anion radicals X-2(-) (X = F, Cl, Br, I). The results indicate that the spin-orbit interaction is responsible for the large parallel component of the g tensor shift of Br-2(-) and I-2(-), and furthermore that both the leading-order scalar relativistic and spin-orbit corrections are of minor importance for the perpendicular component of the g tensor in these molecules since they effectively cancel each other. In addition to investigating the g tensors of dihalogen anion radicals, we also critically examine the importance of various relativistic corrections to the electronic g tensor of linear molecules with Sigma-type ground states and present a two-state model suitable for an approximate estimation of the g tensor in such molecules.
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| 9. |
- Thorvaldsen, Andreas J., et al.
(author)
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Analytic ab initio calculations of coherent anti-Stokes Raman scattering (CARS)
- 2009
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 11:13, s. 2293-2304
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Journal article (peer-reviewed)abstract
- We present a theory for the analytic calculation of frequency-dependent polarizability gradients, and apply the methodology to the calculation of coherent anti-Stokes Raman scattering (CARS). The formalism used is based on an open-ended theory for the calculation of frequency-dependent molecular response properties of arbitrary order, also including contributions from perturbation-dependent basis sets. An important feature of our approach is the close connection between the formalism-which is fully matrix-based in an atomic orbital basis-and the implementation, allowing for the rapid implementation of higher-order molecular properties. Care is taken to allow the formalism to be utilized with linearly-scaling Hartree-Fock and density-functional theory codes. By avoiding the evaluation of responses due to geometry distortions, only 9 response equations need to be solved for the calculation of the CARS intensities, independent of the size of the molecular system. The theory is illustrated by calculations on a set of polyaromatic hydrocarbons using a DFT/B3LYP force field and Hartree-Fock polarizability gradients. Good agreement with the experimental CARS spectra of these compounds is obtained.
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