Improved method of calculatingab initiohigh-temperature thermodynamic properties with application to ZrC

Abstract

Thermodynamic properties of ZrC are calculated up to the melting point (T melt ≈ 3700 K), using density functional theory (DFT) to obtain the fully anharmonic vibrational contribution, and including electronic excitations. A significant improvement is found in comparison to results calculated within the quasiharmonic approximation. The calculated thermal expansion is in better agreement with experiment and the heat capacity reproduces rather closely a CALPHAD estimate. The calculations are presented as an application of a development of the upsampled thermodynamic integration using Langevin dynamics (UP-TILD) approach. This development, referred to here as two-stage upsampled thermodynamic integration using Langevin dynamics (TU-TILD), is the inclusion of tailored interatomic potentials to characterize an intermediate reference state of anharmonic vibrations on a two-stage path of thermodynamic integration between the original DFT quasiharmonic free energy and the fully anharmonic DFT free energy. This approach greatly accelerates the convergence of the calculation, giving a factor of improvement in efficiency of ∼50 in the present case compared to the original UP-TILD approach, and it can be applied to a wide range of materials.

Atomistic Modeling‐Based Design of Novel Materials

“…The near future DFT applications for investigations of material properties and for prediction of novel materials with tailored technological specifications may be foreseen, and has already started, in four basic directions (for each area we provide several references, which coin the path): 1) finite temperature effects, [37,38,125,127,129,[131][132][133][134]160] 2) extended defects (grain boundaries, stacking faults, dislocations, etc. ), [8,98,[193][194][195][196][197][198][199][200][201][202][203][204][205][206][207][208][209] 3) materials of relevance for real applications (complex compositions, realistic conditions, etc.…”

MEAMfit: A reference-free modified embedded atom method (RF-MEAM) energy and force-fitting code

“…The ZrC rocksalt structure is calculated close to its melting temperature (T m ≈ 3800K), with a lattice parameter appropriate to this temperature of a=4.850Å, calculated within the quasiharmonic approximation (using Phonopy [34]). For the exchangecorrelation functional, the LDA rather than the GGA is used, although for a detailed discussion of the reasons for this, as well as a thorough description of all other calculational details, the reader is referred to a forthcoming report [35] (wherein a first application of the potential derived here will also be described).…”

“…A supercell consisting of 2 × 2 × 2 conventional cells is used, [35] with 3 × 3 × 3 Monkhorst Pack k-points sampling and with an energy cut-off of 450eV. With these settings, total energies of supercells are converged to within ± 3 meV per atom.…”

The role of ceramic and glass science research in meeting societal challenges: Report from an NSF‐sponsored workshop

“…Such calculations are much more demanding and not yet generally available, although an early approach for elemental metals was demonstrated in the 1990s by DFT calculations of the melting curve of Fe up to 6000 K in the earth's core, at pressures up to 350 GPa . Progress has since enabled DFT calculations of thermal expansion and heat capacity of pure ZrC up to 3500 K . Although not yet possible, extension of these ideas to the prediction of new materials is encouraging.…”