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SUMMARY:The vibrational spectrum of vitreous silica: rigorous decompositio
 n via recursive orthogonal splitting analysis
DTSTART:20261022T143000Z
DTEND:20261022T153000Z
DTSTAMP:20261023T100700Z
UID:indico-event-1957@indico.dfa.unipd.it
DESCRIPTION:Speakers: Anaël Lemaître (laboratorio Navier - école nation
 ale des ponts et  chaussées (ENPC)\, Parigi)\n\n\n \nSpeaker: prof. Ana
 ël LemaîtreLaboratorio Navier - École Nationale des Ponts et des Chauss
 ées (ENPC)\, ParigiTitle:   The vibrational spectrum of vitreous silica
 : rigorous decomposition via recursive orthogonal splitting analysisAbstra
 ct:Our understanding of vibrations in solids currently rests on concepts a
 nd techniques designed for crystals and explicitly relying on periodicity\
 , hence inapplicable to amorphous materials. As a consequence\, no establi
 shed framework enables a systematic decomposition of the vibrational spect
 rum of amorphous solids into contributions associated with well-defined ty
 pes of atomic motions. This methodological gap obscures the interpretation
  of various experimental probes of linear response\, based on the measurem
 ents of acoustic\, thermal\, or optical properties. Here\, we construct su
 ch a framework---Recursive Orthogonal Splitting Analysis (ROSA)---which de
 composes the vibrational space by recursive applications of the projection
  formalism. Each step of the procedure exploits a dominant stiffness contr
 ast to split a vibrational displacement subspace into two weakly coupled o
 rthogonal complements. We illustrate ROSA by applying it to the archetypal
  covalent glass---vitreous silica. Successively separating bond-stretching
 \, symmetric and antisymmetric oxygen motions\, isotropic and deviatoric t
 etrahedral strains\, and distinct classes of tetrahedral bending\, reveals
  a hierarchical structure of the space of vibrational degrees of freedom\,
  involving six mutually orthogonal subspaces. These subspaces selectively 
 capture all salient spectral features\, including the two-humped structure
  in the low-frequency range\, the peak near 800cm^{-1}\, and the high-freq
 uency doublet. In the low-frequency range\, rigid-unit tetrahedral rotatio
 ns do not constitute independent degrees of freedom but are kinematically 
 enslaved to bending coordinates by no-stretch constraints. Because ROSA re
 lies solely on the existence of contrasted stiffness scales associated wit
 h the point symmetry of local structural units\, and on their separation b
 y enforcing geometric constraints via the projection formalism\, it is dir
 ectly applicable to a broad class of covalent network glasses.\n \n \n 
 \n \n \n \n \n\nhttps://indico.dfa.unipd.it/event/1957/
LOCATION:1/1-2 - Aula "C. Voci" (Dipartimento di Fisica e Astronomia - Edi
 ficio Marzolo)
URL:https://indico.dfa.unipd.it/event/1957/
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