Understanding Anharmonicity in fcc Materials: From its Origin to<i>ab initio</i>Strategies beyond the Quasiharmonic Approximation

Glensk, Albert; Grabowski, Blazej; Hickel, Tilmann; Neugebauer, Jörg

doi:10.1103/physrevlett.114.195901

Cited by 126 publications

(110 citation statements)

References 27 publications

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“…Lattice anharmonicity is also known to cause deviations from an Arrhenius temperature-dependent behavior for thermodynamic and kinetic properties in bulk systems. For example, it is known that vacancy formation [106,107] and migration (or diffusion, i.e., defect formation + defect migration) energies [108][109][110] may vary considerably from 0 K up to the melting temperature. Molecular dynamics simulations inherently resolve the problems mentioned above by integrating Newton's equations of motion for each atom at any temperature of interest.…”

Section: Finite-temperature Aimd Resultsmentioning

confidence: 99%

Effects of surface vibrations on interlayer mass transport: Ab initio molecular dynamics investigation of Ti adatom descent pathways and rates from TiN/TiN(001) islands

et al. 2018

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We carried out density-functional ab initio molecular dynamics (AIMD) simulations of Ti adatom (Ti ad ) migration on, and descent from, square TiN 100 epitaxial islands on TiN(001) at temperatures (T ) ranging from 1200 to 2400 K. Adatom-descent energy barriers determined via ab initio nudged-elastic-band calculations at 0 Kelvin suggest that Ti interlayer transport on TiN(001) occurs essentially exclusively via direct hopping onto a lower layer. However, AIMD simulations reveal comparable rates for Ti ad descent via direct hopping vs push-out/exchange with a Ti island-edge atom for T 1500 K. We demonstrate that this effect is due to surface vibrations, which yield considerably lower activation energies at finite temperatures by significantly modifying the adatom push-out/exchange reaction pathway.

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Section: Finite-temperature Aimd Resultsmentioning

confidence: 99%

Effects of surface vibrations on interlayer mass transport: Ab initio molecular dynamics investigation of Ti adatom descent pathways and rates from TiN/TiN(001) islands

et al. 2018

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“…The insensitivity of high-temperature vibrations to nonlocal many-body effects is remarkable since recent studies [22] showed that close to melting the displacement of atoms from their equilibrium positions is significant and that the first-neighbor distance distribution is strongly affected by anharmonicity. Knowing that the GGA-PBE deficiency is not related to thermal vibrations but rather to the T = 0 K energy surface indicates a possible route for the development of accurate ab initio databases.…”

Section: Fig 2 (Color Online)mentioning

confidence: 99%

“…Recent work [22] showed that explicit anharmonicity can partly compensate the quasiharmonic heat capacity. As shown in Fig.…”

Section: Fig 2 (Color Online)mentioning

confidence: 99%

Random phase approximation up to the melting point: Impact of anharmonicity and nonlocal many-body effects on the thermodynamics of Au

et al. 2015

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Application of the generalized gradient corrected functional within standard density-functional theory results in a dramatic failure for Au, leading to divergent thermodynamic properties well below the melting point. By combining the upsampled thermodynamic integration using Langevin dynamics technique with the random phase approximation, we show that inclusion of nonlocal many-body effects leads to a stabilization and to an excellent agreement with experiment. Most present-day ab initio databases contain results from T = 0 K density-functional-theory (DFT) calculations using standard exchange-correlation functionals. This is a limitation in two respects: (a) First, materials development and application takes place at finite temperatures at which entropic contributions become important. In particular, anharmonic phonon-phonon excitations have been revealed to strongly modify materials properties, e.g., for dynamically unstable systems [2] or for defect formation [3]. (b) Second, standard functionals are known to have intrinsic deficiencies, e.g., for elements with nearly full electron shells. Hybrid functionals provide an improvement by introducing a fraction of exact exchange [4][5][6], but the corresponding mixing parameter is not always well defined, especially for composite systems. Further improvement requires also the correlation energy to include nonlocal many-body effects. A possible route utilizes the random phase approximation (RPA) within the adiabatic-connection-fluctuation-dissipation theorem (ACFDT) [7]. RPA has been successfully applied to various systems [8][9][10] and recent developments aim at improving the computational efficiency [11,12]. However, despite the various developments and applications, RPA has been employed only at T = 0 K, whereas the impact of nonlocal many-body interactions at finite temperatures has remained unknown.In this Rapid Communication, we compute the material properties of Au-a prototype closed shell element-using the RPA within the ACFDT formalism up to the melting point. This is made possible by advancing our previously introduced upsampled thermodynamic integration using Langevin dynamics (UP-TILD) technique [13] towards a combination of molecular dynamics simulations performed at the standard DFT level in conjunction with upsampled snapshots computed within RPA. We shall demonstrate that the inclusion of nonlocal many-body effects remedies the deficiencies introduced by standard DFT.We start by investigating the thermodynamics of Au within the Perdew-Burke-Ernzerhof generalized gradient approximation ) in conjunction with the projectoraugmented-wave (PAW) formalism [15] as implemented in VASP [16,17] using the newly designed GW-PAW potentials [10]. We concentrate on the heat capacity, which is a representative thermodynamic quantity. The state-of-the-art approach to calculate its temperature dependence includes electronic excitations in conjunction with the quasiharmonic approximation. We find that electronic excitations give a negligible contribution [18] due to ...

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“…This is indeed associated with temperature variations of the vibrational entropy in the plane orthogonal to the migration path. Lattice vibrations are known to affect the shape of the effective potential energy landscape, especially at temperatures close to melting [49,50,96]. A separate quantification of the effects of harmonic and anharmonic vibrations on temperature-induced variations in migration energies is a challenging research topic that deserves thoughtful investigation.…”

Section: B Ti Vacancy Equilibrium Jump Ratesmentioning

confidence: 99%

“…Kinetic properties are extrapolated to finite temperatures using transition state theory (TST) [44] by assuming essentially fully harmonic lattice vibrations, or employing quasiharmonic approximations [45,46]. These approaches, however, are not applicable to crystal phases which are unstable at 0 K (e.g., Group-VB TM nitrides [47,48]) and may yield inaccurate predictions when the role of anharmonic lattice vibrations becomes relevant [49][50][51]. Quantitatively reliable evaluation of kinetically controlled properties at given temperatures and pressures of interest necessarily requires the use of computer simulations reproducing atomic trajectories.…”

Section: Introductionmentioning

confidence: 99%

Nonequilibrium ab initio molecular dynamics determination of Ti monovacancy migration rates in B1 TiN

et al. 2017

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We use the color diffusion (CD) algorithm in nonequilibrium (accelerated) ab initio molecular dynamics simulations to determine Ti monovacancy jump frequencies in NaCl-structure titanium nitride (TiN), at temperatures ranging from 2200 to 3000 K. Our results show that the CD method extended beyond the linear-fitting rate-versus-force regime [Sangiovanni et al., Phys. Rev. B 93, 094305 (2016)] can efficiently determine metal vacancy migration rates in TiN, despite the low mobilities of lattice defects in this type of ceramic compound. We propose a computational method based on gamma-distribution statistics, which provides unambiguous definition of nonequilibrium and equilibrium (extrapolated) vacancy jump rates with corresponding statistical uncertainties. The acceleration-factor achieved in our implementation of nonequilibrium molecular dynamics increases dramatically for decreasing temperatures from 500 for T close to the melting point T m , up to 33 000 for T ≈ 0.7 T m .

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Understanding Anharmonicity in fcc Materials: From its Origin toab initioStrategies beyond the Quasiharmonic Approximation

Cited by 126 publications

References 27 publications

Effects of surface vibrations on interlayer mass transport: Ab initio molecular dynamics investigation of Ti adatom descent pathways and rates from TiN/TiN(001) islands

Effects of surface vibrations on interlayer mass transport: Ab initio molecular dynamics investigation of Ti adatom descent pathways and rates from TiN/TiN(001) islands

Random phase approximation up to the melting point: Impact of anharmonicity and nonlocal many-body effects on the thermodynamics of Au

Nonequilibrium ab initio molecular dynamics determination of Ti monovacancy migration rates in B1 TiN

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