Abstract:Rare-gas solids (Ne, Ar, Kr, and Xe) under hydrostatic pressure up to 30 kbar have been studied by path-integral Monte Carlo simulations in the isothermal-isobaric ensemble. Results of these simulations have been compared with available experimental data and with those obtained from a quasiharmonic approximation (QHA). This comparison allows us to quantify the overall anharmonicity of the lattice vibrations and its influence on several structural and thermodynamic properties of rare-gas solids. The vibrational… Show more
“…For example, at T = 20 K and P = 1 GPa, we find for solid 4 He: B = 4.53 GPa, vs 7.20 and 9.43 for Ne and Ar, respectively [30]. This is in line with the known result that the bulk modulus increases with atomic mass for given values of temperature and pressure [30].…”
Section: B Pressure and Temperature Dependencesupporting
The compressibility of solid helium ( 3 He and 4 He) in the hcp and fcc phases has been studied by path-integral Monte Carlo. Simulations were carried out in both canonical (N V T ) and isothermalisobaric (N P T ) ensembles at temperatures between 10 and 300 K, showing consistent results in both ensembles. For pressures between 4 and 10 GPa, the bulk modulus B is found to decrease by about 10%, when temperature increases from the low-temperature limit to the melting temperature. The isotopic effect on the bulk modulus of helium crystals has been quantified in a wide range of parameters. At 25 K and pressures on the order of 1 GPa, the relative difference between 3 He and 4 He amounts to about 2%. The thermal expansion has been also quantified from results obtained in both N P T and N V T simulations.
“…For example, at T = 20 K and P = 1 GPa, we find for solid 4 He: B = 4.53 GPa, vs 7.20 and 9.43 for Ne and Ar, respectively [30]. This is in line with the known result that the bulk modulus increases with atomic mass for given values of temperature and pressure [30].…”
Section: B Pressure and Temperature Dependencesupporting
The compressibility of solid helium ( 3 He and 4 He) in the hcp and fcc phases has been studied by path-integral Monte Carlo. Simulations were carried out in both canonical (N V T ) and isothermalisobaric (N P T ) ensembles at temperatures between 10 and 300 K, showing consistent results in both ensembles. For pressures between 4 and 10 GPa, the bulk modulus B is found to decrease by about 10%, when temperature increases from the low-temperature limit to the melting temperature. The isotopic effect on the bulk modulus of helium crystals has been quantified in a wide range of parameters. At 25 K and pressures on the order of 1 GPa, the relative difference between 3 He and 4 He amounts to about 2%. The thermal expansion has been also quantified from results obtained in both N P T and N V T simulations.
“…Their result for A is in good agreement with the present value (A = 2.88 at 0.53 GPa). With respect to the C 11 , C 12 , and C 44 , we cannot directly compare the elastic properties under low temperature [6,13] with the present ones, because the elastic constants for rare-gas solids strongly depend on the pressure and temperature.…”
The pressure dependences of three adiabatic elastic constants, adiabatic bulk modulus, refractive index, and elastic anisotropy, as well as Cauchy deviation of fcc solid Xe have been determined up to 10 GPa at 296 K by high-pressure Brillouin scattering spectroscopy. The characteristics of elastic properties at high pressure of rare-gas solid Xe are investigated by comparison with the previous studies on Ne, Ar, and Kr. Above 10 GPa, the occurrence of splitting in the Brillouin signals and the direction dependence of acoustic velocities for solid Xe clearly show partial phase transformation to the hcp structure reported by the previous X-ray diffraction and Raman scattering studies. The shear elastic modulus in the hcp phase of solid Xe has also been estimated at pressures up to 45 GPa by using the pressure dependence of the Raman wavenumber shift for the E 2g mode.
“…(67)], which dominates at high pressures. Results of these PIMC simulations indicated that the accuracy of the QHA to describe noble-gas solids increases as pressure is raised 115 . This is mainly a consequence of the relative importance of elastic and vibrational energy, as the latter becomes comparatively irrelevant as pressure rises.…”
Section: B Heavier Elementsmentioning
confidence: 99%
“…For rising Λ, these effective potentials become increasingly softer, shallower, and of longer range, with the potential minimum shifted to larger distances. Given the importance of anharmonic effects in noblegas solids, PIMC simulations have been employed to assess the accuracy of harmonic or quasi-harmonic approximations for vibrational modes in these solids under pressure 115 . This allowed to quantify the overall anharmonicity of the lattice vibrations and its influence on several structural and thermodynamic properties.…”
The path-integral formulation of the statistical mechanics of quantum many-body systems is described, with the purpose of introducing practical techniques for the simulation of solids. Monte Carlo and molecular dynamics methods for distinguishable quantum particles are presented, with particular attention to the isothermal-isobaric ensemble. Applications of these computational techniques to different types of solids are reviewed, including noble-gas solids (helium and heavier elements), group-IV materials (diamond and elemental semiconductors), and molecular solids (with emphasis on hydrogen and ice). Structural, vibrational, and thermodynamic properties of these materials are discussed. Applications also include point defects in solids (structure and diffusion), as well as nuclear quantum effects in solid surfaces and adsorbates. Different phenomena are discussed, as solid-to-solid and orientational phase transitions, rates of quantum processes, classical-to-quantum crossover, and various finite-temperature anharmonic effects (thermal expansion, isotopic effects, electron-phonon interactions). Nuclear quantum effects are most remarkable in the presence of light atoms, so that especial emphasis is laid on solids containing hydrogen as a constituent element or as an impurity.
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