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SUMMARY:Exploring the vibrational properties of anharmonic crystals - Mark
  Johnson (Theory of Condensed Matter)
DTSTART:20201202T113000Z
DTEND:20201202T123000Z
UID:TALK154141@talks.cam.ac.uk
CONTACT:Angela Harper
DESCRIPTION:Calculating the electronic properties of crystals is now routi
 ne\, and\nmany software packages are available for performing these calcul
 ations.\nIn contrast\, calculations of the vibrational properties of cryst
 als are\nfar less developed. When vibrational properties are not neglected
 \nentirely\, they are typically calculated under the harmonic\napproximati
 on. The harmonic approximation makes calculation relatively\nstraightforwa
 rd and inexpensive\, but for many systems this approximation\nis overly re
 strictive\, and there are many crystal properties which it\nentirely fails
  to capture.\n\nThere are a number of anharmonic vibrational methods which
  are widely\nused for calculating the properties of molecular systems\, an
 d in recent\nyears some of these methods have been adapted for use with cr
 ystals.\nHowever\, crystals are not molecules. Unlike molecules\, crystals
  have\ntranslational symmetry\, and many crystals have complex space group
 \nsymmetries. Further\, crystals are extended systems\, and so their\nprop
 erties must be correctly extensive or intensive. Symmetry and\nsize-consis
 tency can be exploited to accelerate crystal models\, and any\nmodel which
  violates these conditions is likely to be inaccurate\, yet\nthese conditi
 ons are not widely recognised in the vibrational modelling\ncommunity.\n\n
 This talk seeks to highlight the importance of symmetry and\nsize-consiste
 ncy to modelling the vibrational properties of crystals\,\nand to present 
 a number of problems with existing models which arise\nwhere these constra
 ints are broken.\n\n\n\nJoin Zoom Meeting: https://bham-ac-uk.zoom.us/j/85
 702415099?pwd=VTh5aFZ4Sm9Nc1dxZXYwelJpc1JtZz09 \n\nMeeting ID: 857 0241 50
 99 \n\nPasscode: 501623
LOCATION:Zoom
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