The Experts below are selected from a list of 7827 Experts worldwide ranked by ideXlab platform
Athanassios Z. Panagiotopoulos - One of the best experts on this subject based on the ideXlab platform.
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Phase equilibria of the modified Buckingham exponential-6 potential from Hamiltonian scaling grand canonical Monte Carlo
1998Co-Authors: Jeffrey R. Errington, Athanassios Z. PanagiotopoulosAbstract:A novel method, Hamiltonian scaling grand canonical Monte Carlo, has been used to determine the phase behavior of 12 variations of the modified Buckingham exponential-6 potential. Hamiltonian scaling grand canonical Monte Carlo enables the determination of thermodynamic properties of several related potential models from a single set of simulations. The main advantage of the method is that by appropriate selection of the chemical potential and temperature for each Hamiltonian, the densities that are sampled are relevant for multiple Hamiltonians, thus increasing the simulation efficiency. The method was combined with mixed-field finite-size scaling to determine the critical parameters and phase coexistence curves of several modified Buckingham exponential-6 potentials to a high level of accuracy. In particular, the critical parameters of the models have been calculated to within 0.3% for the critical temperature and 1% for the critical density and pressure. A new potential for methane based on the Buckingham exponential-6 model is presented. The vapor pressure curve of methane from the Buckingham exponential-6 potential model is much more accurate than is possible with the Lennard-Jones potential model.
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phase equilibria of the modified Buckingham exponential 6 potential from hamiltonian scaling grand canonical monte carlo
1998Co-Authors: Jeffrey R. Errington, Athanassios Z. PanagiotopoulosAbstract:A novel method, Hamiltonian scaling grand canonical Monte Carlo, has been used to determine the phase behavior of 12 variations of the modified Buckingham exponential-6 potential. Hamiltonian scaling grand canonical Monte Carlo enables the determination of thermodynamic properties of several related potential models from a single set of simulations. The main advantage of the method is that by appropriate selection of the chemical potential and temperature for each Hamiltonian, the densities that are sampled are relevant for multiple Hamiltonians, thus increasing the simulation efficiency. The method was combined with mixed-field finite-size scaling to determine the critical parameters and phase coexistence curves of several modified Buckingham exponential-6 potentials to a high level of accuracy. In particular, the critical parameters of the models have been calculated to within 0.3% for the critical temperature and 1% for the critical density and pressure. A new potential for methane based on the Bucking...
Jeffrey R. Errington - One of the best experts on this subject based on the ideXlab platform.
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Phase equilibria of the modified Buckingham exponential-6 potential from Hamiltonian scaling grand canonical Monte Carlo
1998Co-Authors: Jeffrey R. Errington, Athanassios Z. PanagiotopoulosAbstract:A novel method, Hamiltonian scaling grand canonical Monte Carlo, has been used to determine the phase behavior of 12 variations of the modified Buckingham exponential-6 potential. Hamiltonian scaling grand canonical Monte Carlo enables the determination of thermodynamic properties of several related potential models from a single set of simulations. The main advantage of the method is that by appropriate selection of the chemical potential and temperature for each Hamiltonian, the densities that are sampled are relevant for multiple Hamiltonians, thus increasing the simulation efficiency. The method was combined with mixed-field finite-size scaling to determine the critical parameters and phase coexistence curves of several modified Buckingham exponential-6 potentials to a high level of accuracy. In particular, the critical parameters of the models have been calculated to within 0.3% for the critical temperature and 1% for the critical density and pressure. A new potential for methane based on the Buckingham exponential-6 model is presented. The vapor pressure curve of methane from the Buckingham exponential-6 potential model is much more accurate than is possible with the Lennard-Jones potential model.
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phase equilibria of the modified Buckingham exponential 6 potential from hamiltonian scaling grand canonical monte carlo
1998Co-Authors: Jeffrey R. Errington, Athanassios Z. PanagiotopoulosAbstract:A novel method, Hamiltonian scaling grand canonical Monte Carlo, has been used to determine the phase behavior of 12 variations of the modified Buckingham exponential-6 potential. Hamiltonian scaling grand canonical Monte Carlo enables the determination of thermodynamic properties of several related potential models from a single set of simulations. The main advantage of the method is that by appropriate selection of the chemical potential and temperature for each Hamiltonian, the densities that are sampled are relevant for multiple Hamiltonians, thus increasing the simulation efficiency. The method was combined with mixed-field finite-size scaling to determine the critical parameters and phase coexistence curves of several modified Buckingham exponential-6 potentials to a high level of accuracy. In particular, the critical parameters of the models have been calculated to within 0.3% for the critical temperature and 1% for the critical density and pressure. A new potential for methane based on the Bucking...
Antonio Rizzo - One of the best experts on this subject based on the ideXlab platform.
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first order properties and Buckingham birefringence of n2o and ocs a computational re investigation
2012Co-Authors: Sonia Coriani, Cristina Puzzarini, Antonio RizzoAbstract:Prompted by recent experimental reinvestigations of the Buckingham birefringence of CO, CO2, OCS and N2O, we have carried out our own reinvestigation of the relevant first- and second-order properties entering the electric-field-gradient-induced birefringence effect of N2O and OCS by means of state-of-the-art quantum chemical methods. The computed and experimentally derived results remain at significant variance, also in consequence of a remarkable disagreement between the ab initio and the experimental values of the quadrupole moment relative to the centre of the nuclear masses.
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relativistic four component calculations of Buckingham birefringence using london atomic orbitals
2011Co-Authors: Radovan Bast, Kenneth Ruud, Antonio Rizzo, Trygve HelgakerAbstract:We present the first relativistic study of the electric-field-gradient induced birefringence (Buckingham birefringence), with application to the series of molecules CX2 (X = O, S, Se, Te). A recently developed atomic-orbital-driven scheme for the calculation of time-dependent molecular properties using one-, two- and four-component relativistic wave functions (Bast et al. in Chem Phys 356:177, 2009) is extended to first-order frequency-dependent magnetic-field perturbations, using London atomic orbitals to ensure gauge-origin independent results and to improve basis-set convergence. Calculations are presented at the Hartree–Fock and Kohn–Sham levels of theory and results for CO2 and CS2 are compared with previous high-level coupled-cluster calculations. Except for the heaviest member of the series, relativistic effects are small—in particular for the temperature-independent contribution to the birefringence. By contrast, the effects of electron correlation are significant. However, the reliability of standard exchange-correlation functionals in describing Buckingham birefringence remains unclear based on the comparison with high-level coupled-cluster singles-and-doubles calculations.
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analytic calculations of nonlinear mixed electric and magnetic frequency dependent molecular properties using london atomic orbitals Buckingham birefringence
2009Co-Authors: Dmitry Shcherbin, Andreas J Thorvaldsen, Kenneth Ruud, Sonia Coriani, Antonio RizzoAbstract:We present the results of the first gauge-origin independent calculations, carried out at Hartree-Fock level, of the molecular parameters that describe the electric-field-induced linear birefringence, also known as Buckingham birefringence. Focus is in particular on the temperature-independent contribution to the observable. We employ a recently developed analytical scheme for calculating frequency-dependent molecular properties of arbitrary order for self-consistent field methods using basis sets that depend explicitly on the frequency and on the external perturbations. The method is applied to naphthalene, fluorobenzene and furan, three systems for which the Buckingham birefringence has been studied experimentally. It is demonstrated that LAOs lead to significant improvements in the basis set convergence of the temperature-independent contribution to the Buckingham birefringence, and that the results obtained on the basis of aug-cc-pVDZ quality London atomic orbital calculations are closer to the basis set limit than the results obtained on the basis of conventional aug-cc-pVQZ quality calculations. The computed values can be used to correct for the neglect of the temperature-independent higher-order contribution often implied in the derivation of the effective quadrupole moments from experimental measurements of the induced birefringence at a single temperature.
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density functional and electron correlated study of five linear birefringences kerr cotton mouton Buckingham jones and magnetoelectric in gaseous benzene vol 121 pg 8814 2004
2008Co-Authors: Antonio Rizzo, Sonia Coriani, Chiara Cappelli, Branislav Jansik, Dan Jonsson, Pawel Salek, Hans Agren, David J D Wilson, Trygve Helgaker, Jose M JunquerahernandezAbstract:Density-functional and electron correlated study of five linear birefringences-Kerr, Cotton-Mouton, Buckingham, Jones and magnetoelectric-in gaseous benzene (vol 121, pg 8814, 2004)
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An ab initio investigation of the Buckingham birefringence of furan, thiophene, and selenophene in cyclohexane solution
2007Co-Authors: Antonio Rizzo, Luca Frediani, Kenneth RuudAbstract:Using a recently developed quadratic response methodology for the calculation of frequency-dependent third-order properties of molecules in solution, we investigate the Buckingham birefringence of furan, thiophene, and selenophene in cyclohexane solution. These systems are chosen since accurate experimental data are available, allowing for a direct comparison of experimental observations with our theoretical estimates. Our model for describing the solvent effects is based on a dielectric continuum approach for the solvent, and uses a molecule-shaped cavity. Our results show qualitatively different Buckingham constants and effective quadrupole centers calculated with and without the solvent, and only when the solvent is included are the qualitative trends observed experimentally reproduced. It is demonstrated that a significant part of this effect arises from the geometry relaxation of the molecules in the solvent.
Sonia Coriani - One of the best experts on this subject based on the ideXlab platform.
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first order properties and Buckingham birefringence of n2o and ocs a computational re investigation
2012Co-Authors: Sonia Coriani, Cristina Puzzarini, Antonio RizzoAbstract:Prompted by recent experimental reinvestigations of the Buckingham birefringence of CO, CO2, OCS and N2O, we have carried out our own reinvestigation of the relevant first- and second-order properties entering the electric-field-gradient-induced birefringence effect of N2O and OCS by means of state-of-the-art quantum chemical methods. The computed and experimentally derived results remain at significant variance, also in consequence of a remarkable disagreement between the ab initio and the experimental values of the quadrupole moment relative to the centre of the nuclear masses.
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analytic calculations of nonlinear mixed electric and magnetic frequency dependent molecular properties using london atomic orbitals Buckingham birefringence
2009Co-Authors: Dmitry Shcherbin, Andreas J Thorvaldsen, Kenneth Ruud, Sonia Coriani, Antonio RizzoAbstract:We present the results of the first gauge-origin independent calculations, carried out at Hartree-Fock level, of the molecular parameters that describe the electric-field-induced linear birefringence, also known as Buckingham birefringence. Focus is in particular on the temperature-independent contribution to the observable. We employ a recently developed analytical scheme for calculating frequency-dependent molecular properties of arbitrary order for self-consistent field methods using basis sets that depend explicitly on the frequency and on the external perturbations. The method is applied to naphthalene, fluorobenzene and furan, three systems for which the Buckingham birefringence has been studied experimentally. It is demonstrated that LAOs lead to significant improvements in the basis set convergence of the temperature-independent contribution to the Buckingham birefringence, and that the results obtained on the basis of aug-cc-pVDZ quality London atomic orbital calculations are closer to the basis set limit than the results obtained on the basis of conventional aug-cc-pVQZ quality calculations. The computed values can be used to correct for the neglect of the temperature-independent higher-order contribution often implied in the derivation of the effective quadrupole moments from experimental measurements of the induced birefringence at a single temperature.
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density functional and electron correlated study of five linear birefringences kerr cotton mouton Buckingham jones and magnetoelectric in gaseous benzene vol 121 pg 8814 2004
2008Co-Authors: Antonio Rizzo, Sonia Coriani, Chiara Cappelli, Branislav Jansik, Dan Jonsson, Pawel Salek, Hans Agren, David J D Wilson, Trygve Helgaker, Jose M JunquerahernandezAbstract:Density-functional and electron correlated study of five linear birefringences-Kerr, Cotton-Mouton, Buckingham, Jones and magnetoelectric-in gaseous benzene (vol 121, pg 8814, 2004)
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on the electric field gradient induced birefringence and electric quadrupole moment of co n2o and ocs
2003Co-Authors: Sonia Coriani, Antonio Rizzo, Dan Jonsson, Asger Halkier, Jurgen Gauss, Ove ChristiansenAbstract:An ab initio coupled cluster investigation of the electric field gradient induced birefringence of three dipolar linear molecules—CO, N2O, and OCS—is presented. Special emphasis is given to the effect of triple excitations in the cluster operator on the so-called effective quadrupole center as well as to the accurate determination of the molecular electric quadrupole moment relative to this origin. Triple excitations are found to be essential in the case of CO, with reference in particular to the existing disagreement between two semiclassical theories for the interpretation of the experimentally observed birefringence. The present results favor the older theory due to Buckingham and Longuet-Higgins.
Per Moldrup - One of the best experts on this subject based on the ideXlab platform.
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the gas diffusivity based Buckingham tortuosity factor from pf 1 to 6 91 as a soil structure fingerprint
2010Co-Authors: T K K C Deepagoda, Ken Kawamoto, Toshiko Komatsu, Per Moldrup, S Yoshikawa, D E Rolston, R J Gilkes, N PrakongkepAbstract:Subsurface migration of greenhouse gases and other gaseous phase contaminants is predominantly controlled by soil gas diffusion coefficient (Dp) and its variations with soil-air content (e) and soil moisture (or potential) status. Buckingham (1904) stated that Dp is proportional to e X with X characterizing the tortuosity and connectivity of air-filled pore space. In the Buckingham model, as well as many subsequent power-law models, the tortuosity factor, X, is assumed to be constant for a given soil irrespective of its soil potential status. This study shows a marked variation of X with soil matric potential (ψ) given by pF [= log (-ψ, cm H2O)] ranging from 1 to 6.91 for a range of structureless and, in particular, aggregated/structured soils. The X-pF function for aggregated soils showed a monotonic decrease with increasing pF up to pF 3 near which inter-aggregate pores are completely drained, and an increase from pF 3 to pF 6.91 with the draining of intraaggregate pores. Two X(pF) expressions are proposed in order to independently describe the interaggregate tortuosity viz X, (for pF ≤ 3) and intra-aggregate tortuosity, X*, (for 3 ≤ pF ≤ 6.91), These expressions not only yielded better predictions of Dp but also provided useful soil structure fingerprints across a wide range of soil types.
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linear model to predict soil gas diffusivity from two soil water retention points in unsaturated volcanic ash soils
2008Co-Authors: Augustus C Resurreccion, Ken Kawamoto, Toshiko Komatsu, Seiko Yoshikawa, Masanobu Oda, Per MoldrupAbstract:Risk assessment and design of remediation methods at soil sites polluted with gaseous phase contaminant require an accurate description of soil-gas diffusion coefficient (Dp) which is typically governed by the variations in soil air-filled porosity (va). For undisturbed volcanic ash soils, recent studies have shown that a linear Dp(va) model, taking into account inactive air-filled pore space (threshold soil-air content, va, th), captured the Dp data across the total soil moisture range from wet to completely dry conditions. In this study, we developed a simple, easy to apply, and still accurate linear Dp(va) model for undisturbed volcanic ash soils. The model slope C and intercept (interpreted as va, th) were derived using the classical Buckingham (1904) Dp(va) power-law model, vaX, at two soil-water matric potentials of pF 2 (near field capacity condition) and pF 4.1 (near wilting point condition), and assuming the same value for the Buckingham exponent (X=2.3) in agreement with measured data. This linear Dp(va) prediction model performed better than the traditionally-used non-linear Dp(va) models, especially at dry soil conditions, when tested against several independent data sets from literature. Model parameter sensitivity analysis on soil compaction effects showed that a decrease in slope C and va, th due to uniaxial reduction of air-filled pore space in between aggregates markedly affects the magnitude of soil-gas diffusivity. We recommend the new Dp(va) model using only the soil-air contents at two soil-water matric potential conditions (field capacity and wilting point) for a rapid assessment of the entire Dp-va function.
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modeling diffusion and reaction in soils ix the Buckingham burdine campbell equation for gas diffusivity in undisturbed soil
1999Co-Authors: Per Moldrup, Torben Olesen, T Yamaguchi, Per Schjonning, Dennis E RolstonAbstract:Accurate description of gas diffusivity (ratio of gas diffusion coefficients in soil and free air, D s /D 0 ) in undisturbed soils is a prerequisite for predicting in situ transport and fate of volatile organic chemicals and greenhouse gases. Reference point gas diffusivities (R p ) in completely dry soil were estimated for 20 undisturbed soils by assuming a power function relation between gas diffusivity and air-filled porosity (e). Among the classical gas diffusivity models, the Buckingham (1904) expression, equal to the soil total porosity squared, best described R p . Inasmuch as our previous works (Parts III, VII, VIII) implied a soil-type dependency of D s /D 0 (e) in undisturbed soils, the Buckingham R p expression was inserted in two soil- type-dependent D s /D 0 (e) models. One D s /D 0 (e) model is a function of pore-size distribution (the Campbell water retention parameter used in a modified Burdine capillary tube model), and the other is a calibrated, empirical function of soil texture (silt + sand fraction). Both the Buckingham-Burdine-Campbell (BBC) and the Buckingham/soil texture-based D s /D 0 (e) models described well the observed soil type effects on gas diffusivity and gave improved predictions compared with soil type independent models when tested against an independent data set for six undisturbed surface soils (11-46% clay). This study emphasizes that simple but soil-type-dependent power function D s /D 0 (e) models can adequately describe and predict gas diffusivity in undisturbed soil. We recommend the new BBC model as basis for modeling gas transport and reactions in undisturbed soil systems.
