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SUMMARY:Anharmonic phonons and second-order phase-transitions
DTSTART:20170925T131500
DTEND:20170925T141500
DTSTAMP:20260408T134322Z
UID:01a90d5aff393e2c1cf0078cbfeff2b4ec02f44a5f56bb7951f42011
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Francesco Mauri\, Sapienza University\, Rome\nAnharmonic
  effects can generally be treated within perturbation theory. Such an appr
 oach breaks down when the harmonic solution is dynamically unstable or whe
 n the anharmonic corrections of the phonon energies are larger than the ha
 rmonic frequencies themselves. This situation occurs near lattice-related 
 second-order phase-transitions such as charge-density-wave (CDW) or ferroe
 lectric instabilities or in H-containing materials\, where the large zero-
 point motion of the protons results in a violation of the harmonic approxi
 mation. Interestingly\, even in these cases\, phonons can be observed\, me
 asured\, and used to model transport properties. In order to treat such ca
 ses\, we developed a stochastic implementation of the self-consistent harm
 onic approximation valid to treat anharmonicity in the nonperturbative reg
 ime and to obtain\, from first-principles\, the structural\, thermodynamic
  and vibrational properties of strongly anharmonic systems [1\,2]. I will 
 present applications to the ferroelectric transitions in SnTe [2]\, to the
  CWD transitions in NbS2 and NbSe2 (in bulk and monolayer) and to the hydr
 ogen-bond symmetrization transition in the superconducting hydrogen sulfid
 e system [3]\, that exhibits the highest Tc reported for any superconducto
 r so far. In all cases we are able to predict the transition temperature (
 pressure) and the evolution of phonons with temperature (pressure).\n\n[1]
  I. Errea\, M. Calandra\, F. Mauri\, Phys. Rev. Lett. 111\, 177002 (2013) 
 and Phys. Rev. B 89\, 064302 (2014)\n\n[2] R. Bianco\, I. Errea\, L. Paula
 tto\, M. Calandra\, F. Mauri\, Phys. Rev. B 96\, 014111 (2017)\n\n[3] I. E
 rrea\, M. Calandra\, C. J. Pickard\, J. R. Nelson\, R. J. Needs\, Y. Li\, 
 H. Liu\, Y. Zhang\, Y. Ma\, F. Mauri\, Nature 532\, 81 (2016)\n\nBio: Prof
 essor Francesco Mauri is a Full Professor at the Sapienza University. Foll
 owing a master’s degree in physics from the University of Pisa and Scuol
 a Normale Superiore\, he obtained his PhD from Université de Geneva\, and
  from Sissa in Trieste in 2000. Following postdoctoral stays as Miller Fel
 low at University of California\, Berkeley\, he obtained a Full professors
 hip at the Université Pierre et Marie Curie in Paris in 1998. He moved to
  Rome at Sapienza in 2015. He is an expert in the description of physical 
 properties of materials by first-principles electronic structure methods\,
  with emphasis on the simulation of spectroscopy data (NMR\, EPR\, Raman\,
  IR\, Xanes)\, on the electron-phonon and phonon-phonon interactions\, on 
 the thermal and electronic transport\, on superconductivity\, on graphene 
 and 2D materials.
LOCATION:MXF 1 https://plan.epfl.ch/?room==MXF%201
STATUS:CONFIRMED
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