Thermal conductivity of argon at high pressure from first principles calculations

Abstract

We present calculations of the thermal conductivity of fcc Argon at high pressures (pressure range is 10-150 GPa, temperatures range is 400-1200 K) from first principles in the framework of density functional theory and solution of the Boltzmann Transport Equation. Local density approximation (LDA) and generalized gradient approximation (GGA) produce similar thermal conductivities, with differences accounted by the known overbinding and underbinding of the LDA and GGA, correspondingly. Thermal conductivities at all considered pressures and temperatures are found to be consistent with the results of previous molecular dynamics simulations based on classical 2-body potentials. However, they are not consistent with recent experimental findings. Possible reasons for this disagreement are discussed. In addition, in light of our calculations, we critically examine analytically tractable approximations for thermal conductivity as applied to solid argon. V C 2013 AIP Publishing LLC. [http://dx.

Origins of thermal conductivity changes in strained crystals

“…Using a diamond anvil cell, argon was compressed in the stress range of 10 to 50 GPa. They found a power-law dependence of thermal conductivity with increasing compression at a temperature of 300 K. Chernatynskiy and Phillpot explored high-temperature (400 to 1200 K) argon using harmonic and anharmonic lattice dynamics calculations with force constants obtained from density functional theory (DFT) calculations over a compressive stress range of 10 to 50 GPa [18]. Their thermal conductivity predictions fit the power-law functional form proposed by Tretiakov and Scandolo [15].…”

Anharmonic properties inMg2X(X=C,SiChernatynskiy1, Phillpot2 2015Phys. Rev. BSelf Cite18280View full textAdd to dashboardCite

“…The individual phonon lifetimes, Figure 7, show the general features that have being discussed in other materials. 19,20 Namely, the low frequency part of the spectrum can be fitted reasonably well with a second degree polynomial; however, at higher frequencies the dependence is, in fact, non-monotonic. A surprising feature, however, is the comparison between different materials: for the entire series of Mg 2 X compounds, the phonon lifetime bands overlap with each-other and do not show significant differences.…”

“…It results in very close agreement for Mg 2 Si while producing values substantially lower than both LDA and experiment for Mg 2 Ge. In the previous work by the authors on thermal transport in solid argon such underestimation was attributed to the volume effect 20 , as PBE tends to produce larger equilibrium volume than LDA, which in turn results in softer phonon modes and lower thermal conductivity. While this is the case for Mg 2 Ge, in Mg 2 Si only the two highest optical modes appear to be softer within PBE as compared with LDA calculations.…”

“…Comparison with the experimental data, which also has some scatter, shows that that PBE consistently overestimate the lattice constant, while LDA underestimates, with LDA overall providing somewhat smaller error. The issue of having an accurate lattice constant is important due to the sensitivity of the thermal conductivity to the simulation volume, 20 as we discuss in detail below. Therefore, we use the LDA density functional in the reminder of this work.…”

“…This approach has been used extensively over the last few years to produce quantitatively accurate results for the thermal conductivity of a number of materials. [13][14][15][17][18][19][20][21] We investigate the details of the thermal transport and demonstrate that optical modes are also important in this series of compounds. Further, we investigate the importance of isotopic disorder in these materials.…”