<i>Ab initio</i>potential energy curve for the neon atom pair and thermophysical properties for the dilute neon gas. II. Thermophysical properties for low-density neon

Vogel

2008

Self Cite

104

A six-dimensional potential energy hypersurface (PES) for two interacting rigid methane molecules was determined from high-level quantum-mechanical ab initio computations. A total of 272 points for 17 different angular orientations on the PES were calculated utilizing the counterpoise-corrected supermolecular approach at the CCSD(T) level of theory with basis sets of aug-cc-pVTZ and aug-cc-pVQZ qualities. The calculated interaction energies were extrapolated to the complete basis set limit. An analytical site-site potential function with nine sites per methane molecule was fitted to the interaction energies. In addition, a semiempirical correction to the analytical potential function was introduced to take into account the effects of zero-point vibrations. This correction includes adjustments of the dispersion coefficients and of a single-parameter within the fit to the measured values of the second virial coefficient B(T) at room temperature. Quantitative agreement was then obtained with the measured B values over the whole temperature range of the measurements. The calculated B values should definitely be more reliable at very low temperatures (T<150 K) than values extrapolated using the currently recommended equation of state.

Section: Adjustment Of the Intermolecular Potential Energy Surfacsupporting

confidence: 88%

Ab initio intermolecular potential energy surface and second pressure virial coefficients of methane

Vogel

2008

Self Cite

104

“…The differences from the reliable data of May et al 47 and Schley et al 45 are due to a temperature measurement error in the experiments of Kestin and co-workers with their hightemperature oscillating-disk viscometer. 65 This error was extensively discussed by Vogel et al 44 and was confirmed by comparison of standard viscosity values for helium 52 and neon, 66 obtained from ab initio calculations and using the appropriate kinetic theory, with viscosity data of these gases measured by Kestin and co-workers using the same viscometer. Figure 2 illustrates also that the experimental values of Evers et al 46 are too high by about 0.5%-0.6% compared to the experimental data of May et al, 47 Schley et al, 45 Kestin and Yata, 53 and Kestin et al 55 Although the results of the measurements on helium and neon reported by Evers et al 46 in the same paper are in excellent agreement with the reliable data of other investigators ͑see Refs.…”

Section: Comparison With Experimentsmentioning

confidence: 65%

Calculation of the transport and relaxation properties of methane. I. Shear viscosity, viscomagnetic effects, and self-diffusion

Vogel

et al. 2008

Self Cite

Transport properties of pure methane gas have been calculated in the rigid-rotor approximation using the recently proposed intermolecular potential energy hypersurface [R. Hellmann et al., J. Chem. Phys. 128, 214303 (2008)] and the classical-trajectory method. Results are reported in the dilute-gas limit for shear viscosity, viscomagnetic coefficients, and self-diffusion in the temperature range of 80-1500 K. Compared with the best measurements, the calculated viscosity values are about 0.5% too high at room temperature, although the temperature dependence of the calculated values is in very good agreement with experiment between 210 and 390 K. For the shear viscosity, the calculations indicate that the corrections in the second-order approximation and those due to the angular-momentum polarization are small, less than 0.7%, in the temperature range considered. The very good agreement of the calculated values with the experimental viscosity data suggests that the rigid-rotor approximation should be very reasonable for the three properties considered. In general, the agreement for the other measured properties is within the experimental error.

“…4,5 For neon, our group developed a pair potential of reference quality, 6 and later we 7,8 as well as Patkowski and Szalewicz 9 thoroughly investigated the argon dimer potential. The derived thermophysical property data for gaseous neon 10 and argon 11,12 again show reference character, although their estimated uncertainties are considerably larger than those for helium due to the less accurate quantumchemical approaches feasible for neon and argon. a) Electronic mail: benjamin.jaeger@uni-rostock.de b) Electronic mail: robert.hellmann@uni-rostock.de For a long time, the reference potential for the krypton dimer has been the empirical potential energy curve of Aziz and co-workers 13,14 with a well depth of "/k B = 201.3 K, where k B is Boltzmann's constant.…”

Section: Introductionmentioning

confidence: 91%

State-of-the-art ab initio potential energy curve for the krypton atom pair and thermophysical properties of dilute krypton gas

Jäger

et al. 2016

Self Cite

A new reference krypton-krypton interatomic potential energy curve was developed by means of quantum-chemical ab initio calculations for 36 interatomic separations. Highly accurate values for the interaction energies at the complete basis set limit were obtained using the coupled-cluster method with single, double, and perturbative triple excitations as well as t-aug-cc-pV5Z and t-aug-cc-pV6Z basis sets including mid-bond functions, with the 6Z basis set being newly constructed for this study. Higher orders of coupled-cluster terms were considered in a successive scheme up to full quadruple excitations. Core-core and core-valence correlation effects were included. Furthermore, relativistic effects were studied not only at a scalar relativistic level using second-order direct perturbation theory, but also utilizing full four-component and Gaunt-effect computations. An analytical pair potential function was fitted to the interaction energies, which is characterized by a depth of 200.88 K with an estimated standard uncertainty of 0.51 K. Thermophysical properties of low-density krypton were calculated for temperatures up to 5000 K. Second and third virial coefficients were obtained from statistical thermodynamics. Viscosity and thermal conductivity as well as the self-diffusion coefficient were computed using the kinetic theory of gases. The theoretical results are compared with experimental data and with results for other pair potential functions from the literature, especially with those calculated from the recently developed ab initio potential of Waldrop et al. [J. Chem. Phys. 142, 204307 (2015)]. Highly accurate experimental viscosity data indicate that both the present ab initio pair potential and the one of Waldrop et al. can be regarded as reference potentials, even though the quantum-chemical methods and basis sets differ. However, the uncertainties of the present potential and of the derived properties are estimated to be considerably lower.