Phonon related properties of transition metals, their carbides, and nitrides: A first-principles study

Isaev, É. I.; Simak, Sergei I.; Abrikosov, Igor A.; Ahuja, Rajeev; Vekilov, Yu. Kh.; Katsnelson, M. I.; Lichtenstein, A. I.; Johansson, Börje

doi:10.1063/1.2747230

Cited by 344 publications

(227 citation statements)

References 150 publications

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“…The comparison with the results obtained in coherent neutron inelastic scattering experiments [24] showed a very good agreement between experimental and theoretical results in the acoustic part of the spectrum while for the optical parts there is still some disagreement along all high symmetry directions. Such kind of disagreement between theoretical and experimental optical modes was found previously for some carbides and nitrides of transition metals [25][26][27]. This disagreement between experimental and theoretical optical modes may be caused by the hydrogen anharmonicity.…”

Section: Resultsmentioning

confidence: 71%

Dynamic stability of palladium hydride: An ab initio study

Isaeva

Бажанов

Isaev

et al. 2011

International Journal of Hydrogen Energy

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We present results of our ab initio studies of electronic and dynamic properties of ideal palladium hydride PdH and its vacancy ordered defect phase Pd 3 VacH 4 with L1 2 crystal structure proposed theoretically and found experimentally. Quantum and electronic properties of these hydrides, such as phonon dispersion relations and the vacancy formation enthalpies have been studied. Dynamic stability of the defect phase Pd 3 VacH 4 with respect to different site occupation of hydrogen atoms at the equilibrium state and under pressure was analyzed. It was shown that positions of hydrogen atoms in the defect phase strongly affect its stability and may be a reason for further phase transitions in the defect phase.

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Section: Resultsmentioning

confidence: 71%

Dynamic stability of palladium hydride: An ab initio study

Isaeva

Бажанов

Isaev

et al. 2011

International Journal of Hydrogen Energy

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“…We were led to look at the niobium hydrides in particular by the following additional observation: it is well known that the transition metal Nb holds the record for the highest superconducting transition temperature T c (9.3 K) of an element at normal pressure, 10 and compounds of Nb, such as Nb 3 Ge (23 K), 11 NbC (11 K), 12 and NbN (16 K), 13 also have the highest T c values for their respective classes. There is nothing obvious that distinguishes Nb in the key factors that enter, say, into a BCS estimate of the T c for Nb, NbN, NbC, NbO, or Nb 3 Ge.…”

Section: Introductionmentioning

confidence: 99%

Theoretical study of the ground-state structures and properties of niobium hydrides under pressure

et al. 2013

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As part of a search for enhanced superconductivity, we explore theoretically the ground-state structures and properties of some hydrides of niobium over a range of pressures and particularly those with significant hydrogen content. A primary motivation originates with the observation that under normal conditions niobium is the element with the highest superconducting transition temperature (T c ), and moreover some of its compounds are metals again with very high T c 's. Accordingly, combinations of niobium with hydrogen, with its high dynamic energy scale, are also of considerable interest. This is reinforced further by the suggestion that close to its insulator-metal transition, hydrogen may be induced to enter the metallic state somewhat prematurely by the addition of a relatively small concentration of a suitable transition metal. Here, the methods used correctly reproduce some ground-state structures of niobium hydrides at even higher concentrations of niobium. Interestingly, the particular stoichiometries represented by NbH 4 and NbH 6 are stabilized at fairly low pressures when proton zero-point energies are included. While no paired H 2 units are found in any of the hydrides we have studied up to 400 GPa, we do find complex and interesting networks of hydrogens around the niobiums in high-pressure NbH 6 . The Nb-Nb separations in NbH n are consistently larger than those found in Nb metal at the respective pressures. The structures found in the ground states of the high hydrides, many of them metallic, suggest that the coordination number of hydrogens around each niobium atom grows approximately as 4n in NbH n (n = 1-4), and is as high as 20 in NbH 6 . NbH 4 is found to be a plausible candidate to become a superconductor at high pressure, with an estimated T c ∼ 38 K at 300 GPa.

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“…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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Phonon related properties of transition metals, their carbides, and nitrides: A first-principles study

Cited by 344 publications

References 150 publications

Dynamic stability of palladium hydride: An ab initio study

Dynamic stability of palladium hydride: An ab initio study

Theoretical study of the ground-state structures and properties of niobium hydrides under pressure

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

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