Testing predictions from density functional theory at finite temperatures:β2-like ground states in Co-Pt

Abstract

We perform a critical assessment of the accuracy of DFT-based methods in predicting stable phases within the Co-Pt binary alloy. Statistical mechanical analysis applied to zero kelvin DFT predictions yields finite-temperature results that can be directly compared with experimental measurements. The predicted temperature-composition phase diagram is qualitatively incompatible with experimental observations, indicating that the predicted stability of long-period superstructures as ground states in the Co-Pt binary is incorrect. We also show that recently suggested methods to better align DFT and experiment via the hybrid functional HSE06 are unable to resolve the discrepancies in this system. Our results indicate a need for better verification of DFT based phase stability predictions, and highlight fundamental flaws in the ability of DFT to treat late 3d -5d binary alloys.

Gradient-level and nonlocal density functional descriptions of Cu-Au intermetallic compounds

“…Similar problems with the magnitudes of formation energies and the β 2 structure stability has recently been reported also for the Co-Pt system [7] and the authors of that paper speculate that related alloys, such as Fe-Pt, Ni-Pt, Fe-Ni, are likely to be plagued by the same or similar issues. Recently, Zhang et al have shown that nonlocal hybrid functionals, such as the Heyd-Scuseria-Ernzerhof (HSE06, but hereafter just HSE) [15,16], can effectively fix both the formation energy and the phase stability problems in Cu-Au.…”

“…We also notice that HSE and PBE0 predict almost identical formation energies, which could indicate that Cu-Au is not very sensitive to the screening length details of the HSE functional. For example, Co-Pt has been reported to be a problematic system for HSE due to the unsuitability of the standard HSE screening length for Co [7]. The above findings suggest that one-iteration hybrids can be a viable alternative to the much slower fully self-consistent hybrid calculations, at least for the properties and the type of systems considered here.…”

“…There are, however, many interesting situations that expose the weaknesses of currently popular DFT approximations [4]. In the realm of alloy theory one of the major challenges for DFT is the ability to predict accurate formation energies and phase stabilities that would even qualitatively agree with experimental findings [5][6][7][8]. One notable example is the Cu-Au binary alloy system for which the standard exchange-correlation (XC) approximations, the local density approximation (LDA) [2,9,10] and the semilocal Perdew-Burke-Ernzerhof (PBE) [11] generalized gradient approximation (GGA) [12][13][14], first of all predict formation energies that are too small in magnitude, by nearly a factor of two [5,6,8].…”

Cysteine containing dipeptides show a metal specificity that matches the composition of seawater

“…Difficulties with DFT calculations were shown in the past for complexes containing two interacting transition metals. 9 Mononuclear metal centres are much simpler. Furthermore, calculations using B3LYP were approximately two-fold faster than by using PW91 and PBE0 and showed only slight differences in energies between 0.016% and 0.042% ( Fig.…”

Machine-learning the configurational energy of multicomponent crystalline solids

“…In this way, complex energy landscapes as a function of configurational degrees of freedom can be reproduced by fitting to a relatively small number of first-principles electronic structure calculations. The approach has enabled accurate first-principles predictions of temperature-composition phase diagrams, [23][24][25][26][27][28][29][30][31][32][33][34] order-disorder phenomena, [35][36][37][38][39][40][41][42][43][44][45] and composition-dependent diffusion coefficients in alloys and complex inorganic compounds. [46][47][48][49][50][51][52] A cluster expansion is formulated as a linear series of cluster basis functions multiplied by constant expansion coefficients that are determined by the underlying chemistry and crystal structure of the multicomponent solid.…”