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Computation 2018, 6(2), 29; https://doi.org/10.3390/computation6020029

Kohn Anomaly and Phase Stability in Group VB Transition Metals

1
Physics Division, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA
2
Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA
3
Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
4
Wigner Research Center for Physics, Institute for Solid State Physics and Optics, PO Box 49, H-1525 Budapest, Hungary
5
Department of Physics and Astrinomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden
*
Author to whom correspondence should be addressed.
Received: 28 February 2018 / Revised: 17 March 2018 / Accepted: 21 March 2018 / Published: 26 March 2018
(This article belongs to the Special Issue In Memory of Walter Kohn—Advances in Density Functional Theory)
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Abstract

In the periodic table, only a few pure metals exhibit lattice or magnetic instabilities associated with Fermi surface nesting, the classical examples being α-U and Cr. Whereas α-U displays a strong Kohn anomaly in the phonon spectrum that ultimately leads to the formation of charge density waves (CDWs), Cr is known for its nesting-induced spin density waves (SDWs). Recently, it has become clear that a pronounced Kohn anomaly and the corresponding softening in the elastic constants is also the key factor that controls structural transformations and mechanical properties in compressed group VB metals—materials with relatively high superconducting critical temperatures. This article reviews the current understanding of the structural and mechanical behavior of these metals under pressure with an introduction to the concept of the Kohn anomaly and how it is related to the important concept of Peierls instability. We review both experimental and theoretical results showing different manifestations of the Kohn anomaly in the transverse acoustic phonon mode TA (ξ00) in V, Nb, and Ta. Specifically, in V the anomaly triggers a structural transition to a rhombohedral phase, whereas in Nb and Ta it leads to an anomalous reduction in yield strength. View Full-Text
Keywords: Kohn anomaly; Fermi surface nesting; phonon softening Kohn anomaly; Fermi surface nesting; phonon softening
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Landa, A.; Söderlind, P.; Naumov, I.I.; Klepeis, J.E.; Vitos, L. Kohn Anomaly and Phase Stability in Group VB Transition Metals. Computation 2018, 6, 29.

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