Ab initiovirial equation of state for argon using a new nonadditive three-body potential (original) (raw)
Related papers
Ab initiovirial equation of state for argon using a new nonadditive three-body potential
Journal of Chemical Physics, 2011
An ab initio nonadditive three-body potential for argon has been developed using quantum-chemical calculations at the CCSD(T) and CCSDT levels of theory. Applying this potential together with a recent ab initio pair potential from the literature, the third and fourth to seventh pressure virial coefficients of argon were computed by standard numerical integration and the Mayer-sampling Monte Carlo method, respectively, for a wide temperature range. All calculated virial coefficients were fitted separately as polynomials in temperature. The results for the third virial coefficient agree with values evaluated directly from experimental data and with those computed for other nonadditive three-body potentials. We also redetermined the second and third virial coefficients from the best experimental pρT data utilizing the computed higher virial coefficients as constraints. Thus, a significantly closer agreement of the calculated third virial coefficients with the experimental data was achieved. For different orders of the virial expansion, pρT data have been calculated and compared with results from high quality measurements in the gaseous and supercritical region. The theoretically predicted pressures are within the very small experimental errors of ±0.02% for p 12 MPa in the supercritical region near room temperature, whereas for subcritical temperatures the deviations increase up to +0.3%. The computed pressure at the critical density and temperature is about 1.3% below the experimental value. At pressures between 200 MPa and 1000 MPa and at 373 K, the calculated values deviate by 1% to 9% from the experimental results.
Third Virial Coefficients of Argon from First Principles
Journal of Physical Chemistry C 111(43), 15565, 2007
Third virial coefficients of argon have been calculated using a recent ab initio state-of-the-art pair potential and a new ab initio three-body potential. The theoretical results have been compared with experimental data in the range of temperatures from 130 to 673 K. The comparison reveals an excellent agreement between the theoretical and the newest experimental results: For all considered temperatures, differences between the theoretical and the experimental values are within uncertainties of the experimental data. The theoretical third virial coefficients reported in this work are also compared with those obtained using alternative theoretical approaches.
Molecular Physics, 2003
The internal energies and compressibility factors of argon, krypton and xenon have been simulated using recent state-of-the-art ab initio pair intermolecular potentials and the best semi-empirical pair potentials, and the Axilrod-Teller-Muto three-body term. The results are compared with experimental data for both sub-critical and super-critical temperatures and for densities ranging up to a 2.5 multiple of the critical density. Both the ab initio and semi-empirical results for argon are in very good agreement with the experimental ones. For krypton and xenon, the ab initio results are worse than the semi-empirical results but they are still acceptable.
The Journal of Chemical Physics, 2001
The prediction of the structural and thermodynamic properties of supercritical argon has been carried out by two independent routes: semianalytical calculations and numerical simulations. The first one is based on the hybridized mean spherical approximation ͑HMSA͒ conjugated with an effective pair potential that incorporates multipole dispersion interactions. The second one uses a very recent numerical simulation technique, inspired by the Car-Parrinello method ͓van der Hoef et al., J. Chem. Phys. 111, 1520 ͑1999͔͒, which contains an effective quantum-mechanical representation of the underlying electronic structure. The latter approach allows us to treat the contribution of the three-body effects as well, and to validate the use of an effective pair potential for them in the framework of the self-consistent integral equation method. For all the supercritical argon states studied, the results obtained with the semianalytical approach are in good agreement with the predictions of the numerical simulation. Here it is shown that HMSA remains competitive with molecular dynamics simulation when the triple-dipole and the dipole-dipole-quadrupole three-body terms are taken into account.
Thermodynamics and Molecular Dynamic Simulations of Three-phase Equilibrium in Argon (v8)
Journal of Computer Chemistry, Japan, 2014
Equations of state (EoSs) are proposed for a system consisting of a perfect solid and a perfect liquid made up of single spherical molecules. the Lennard-Jones interaction is assumed for this system. molecular dynamics simulations are performed in order to determine the temperature and density dependences of the internal energy and pressure. the supercooled liquid state is also examined. the internal energy term in the EoSs is the sum of the average kinetic and potential energies at 0 K and the temperature-dependent potential energy. the temperature-dependent term of the average potential energy is assumed to be a linear function of temperature, and its coefficient is expressed as a polynomial function of the number density. The pressure is expressed in a similar manner, where the pressure satisfies the thermodynamic EoS. the equilibrium condition is solved numerically for the phase equilibrium of argon. the Gibbs energy provides a reasonable transition pressure for three-phase equilibrium in argon. the thermodynamic properties at low pressures have significant temperature dependences. The linear character of the pressure and internal energy as functions of temperature in the condensed phases is discussed based on the short-term vibration motion.
Third virial coefficient of nonpolar gases from accurate binary potentials and ternary forces
An explicit model for the third virial coefficient C(T) is presented, based on accurate binary interactions plus three-body forces; its predictions are compared to experimental data for 15 fluids (argon, krypton, xenon, nitrogen, oxygen, fluorine, carbon monoxide, carbon dioxide, perfluoromethane, methane, ethene, ethane, propane, n-butane, and n-pentane). Three-body interactions are represented by the Axilrod–Teller–Muto (ATM) triple-dipole potential, while the binary potential profile is systematically varied using approximate non-conformal (ANC) potentials. Non-conformality affects significantly both two-and three-body contributions to C(T). A formula for C(T) of ANC+ATM systems is obtained in terms of all interaction parameters; the three-body contribution is proportional to the parameter ν of the ATM potential while its temperature dependence is proportional to that of a reference fluid (argon). The ANC+ATM model reproduces C(T) within experimental error for most of the fluids considered, with a small negative deviation in some cases, which may be ascribed to the need of a complement to the ATM term.
We developed an explicit equation of state (EOS) for small non polar molecules by means of an effective two-body potential. The average effect of three-body forces was incorporated as a perturbation, which results in rescaled values for the parameters of the two-body potential. These values replace the original ones in the EOS corresponding to the two-body interaction. We applied this procedure to the heavier noble gases and used a modified Kihara function with an effective Axilrod-Teller-Muto (ATM) term to represent the two-and three-body forces. We also performed molecular dynamics simulations with two-and three-body forces. There was good agreement between predicted, simulated , and experimental thermodynamic properties of neon, argon, krypton, and xenon, up to twice the critical density and up to five times the critical temperature. In order to achieve 1% accuracy of the pressure at liquid densities, the EOS must incorporate the effect of ATM forces. The ATM factor in the rescaled two-body energy is most important at temperatures around and lower than the critical one. Nonetheless, the rescaling of two-body diameter cannot be neglected at liquid-like densities even at high temperature. This methodology can be extended straightforwardly to deal with other two-and three-body potentials. It could also be used for other nonpolar substances where a spherical two-body potential is still a reasonable coarse-grain approximation.
Second virial coefficient for real gases at high temperature
We study the second virial coefficient, B(T ), for simple real gases at high temperature. Theoretical arguments imply that there exists a certain temperature, T i , for each gas, for which this coefficient is a maximum. However, the experimental data clearly exhibits this maximum only for the Helium gas. We argue that this is so because few experimental data are known in the region where these maxima should appear for other gases. We make different assumptions to estimate T i . First, we adopt an empirical formulae for B(T ). Secondly, we assume that the intermolecular potential is the Lennard-Jones one and later we interpolate the known experimental data of B(T ) for Ar, He, Kr, H 2 , N 2 , O 2 , Ne and Xe with simple polynomials of arbitrary powers, combined or not with exponentials. With this assumptions we estimate the values of T i for these gases and compare them.
Journal of Mathematical Chemistry, 2012
In this project we evaluate second virial coefficient of some inert gases via classical cluster expansion, assuming each atomic pair interaction is of Lennard-Jones type. We also try to numerically evaluate the third virial coefficient of Argon gas based on bipolar-coordinate integration (Mas et al. in J Chem Phys 10:6694, 1999), assuming the same Lennard-Jones potential as before. The second virial coefficient (Vega et al. in Phys Chem Chem Phys 4:3000-3007, 2002) calculated from our model are compatible to the experimental data [19] The temperature at which B 2 (T) → 0 is called the Boyle's temperature T B (Vega et al. in Phys Chem Chem Phys 4:3000-3007, 2002) for the Lennard-Jines (12-6) potential. For the second virial coefficient of He, we obtain the Boyle's temperature as follow: T B = 34.9312438964844 (K) B 2 (T) = 9.82958 × 10 −6 (cm 3 /mol).