A study of solid and liquid carbon tetrafluoride using the constant pressure molecular dynamics technique

Abstract

The constant pressure molecular dynamics technique originally proposed by Andersen to study fluids and subsequently generalized by Parrinello and Rahman to deal with crystals of arbitrary symmetry has been further extended to treat molecular systems. As a pedagogical example designed to illustrate the utility of this approach, we have investigated the properties of carbon tetrafluoride in its condensed phases using an intermolecular potential based upon atom–atom interactions. In particular, we have explored the effect of changes in temperature and pressure on the orientationally ordered low temperature monoclinic solid. As in the real crystal, isobaric heating to sufficiently high temperature causes the ordered phase to transform spontaneously to a noncubic orientationally disordered phase. The properties of this disordered phase are also examined along with those of the liquid. The atom–atom potential appears to correlate a wide range of experimental data. The possible role of the electrostatic octopole–octopole interactions is also discussed briefly.

Study of cluster formation in low-temperature systems. Spectral manifestation of resonance dipole–dipole interactions between nondipole polyatomic molecules

“…The calculations using the RDD interaction model are in good agreement with the experimental data on the spectra of low-temperature matrices (CF 4 /Ar (Ne), SF 6 /Ar (Xe, N 2 ), and SiF 4 /Ar (Xe, N 2 ) at 4,7 (11) K), of low-temperature liquids (CF 4 at 90-130 K, SF 6 at 222 K, NF 3 at 90 K, OCS at 135 K, CO 2 , CF 3 Br, CF 3 CL, and BF 3 ), and of their solutions in cryosolvents (Ar at 90-130 K, O 2 at 90-130 K, N 2 at 77-130 K, Kr at 143 K, and Xe at 175 K). The RDD interaction is shown to manifest itself not only in the fundamental bands which are intense in the IR absorption, but also in the overtone and combination bands which include the strongly IR-active fundamental.…”

“…At the same time, the absorption bands in the spectra of pure liquids exhibit complex asymmetric profiles extending over ≈ 60 cm −1 . It seems likely that the main mechanism of the band shape formation is the RDD interaction because the dipole moment derivative 3 P′ has a high value of 0.55 D for SF 6 and 4 . In addition, it can be seen from Figs.…”

“…The intense fundamental band and overtone bands for a mode with a large value of P′ in the IR absorption are asymmetrically broadened by RDD interaction in the Raman [12−14] and IR absorption spectra of lowtemperature molecular liquids consisting of polar or nonpolar molecules [15−17]. By using the RDD interaction formalism, band shape simulations were performed for the absorption spectra of several liquids (CF 4 , SF 6 , SiF 4 , CF 3 Cl and CF 3 Br) at temperatures close to the melting point [18], and the results obtained are in quantitative agreement with the experimental data.…”

Diffusion and mass transfer in supercritical fluids

“…The lack of fundamental significance for the sitesite parameter values is clearly shown from the fact that F-F (Singer, et al, 1977) and C-C (Murad and Gubbins, 1978) parameters had to be significantly altered (Nose and Klein, 1983) to fit the volumetric properties of CF,.…”

New theoretical insight into the interactions and properties of formic acid: Development of a quantum-based pair potential for formic acid

“…36 The equations of motion were integrated using the Verlet algorithm 37 with a time step of 1.0 fs. A Nose-Hoover-type thermostat 38 with a relaxation time of 0.1 ps was used to control the temperature, and the pressure was controlled isotropically. 39 The particle-particle particle-mesh Ewald (PPPM) method 40 (the accuracy criterion was set to 1x10 -5 and the near-field cutoff to 10.0 Å) was used for the long-range correction of electrostatic interactions.…”