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SUMMARY:Understanding Metallic Bonding - Volker Heine
DTSTART:20230209T140000Z
DTEND:20230209T150000Z
UID:TALK196039@talks.cam.ac.uk
CONTACT:Bo Peng
DESCRIPTION:The inter-atomic bonds in metals are (I) strong covalent bonds
 \, but (II) metals are malleable and ductile\, with the bonding structure 
 re-arranging rather easily. (III) Metals usually have one of the closely p
 acked crystal structure\, and (IV) often have phase transitions between th
 em at rather modest temperatures or pressures. (V) The formation energy of
  an atomic vacancy is only about *half* of what one might expect from coun
 ting the net number of broken bonds. (VI) Metals tend to speed up and chan
 ge chemical reactions (catalysis) at their surfaces.\n\nAll the above can 
 be found and explained in a simple model\, but treated rigorously quantum 
 mechanically\, for a metal of one type of electron (e.g. atomic s-electron
 s or d-electrons) only\, the latter being quite a good approximation for t
 he transition metals. A short quantum mechanical calculation shows the ene
 rgy to be proportional to the *square root*  of the coordination number C 
 of near neighbours\, which accounts for the properties II to VI. Total ene
 rgy calculations for aluminium with its mixture of atomic 3s and 3p electr
 ons are found to give similar results.\n\nThe analysis shows that a metal 
 atom is bonded to its surrounding cluster of close neighbours as a whole i
 n a 'cluster bond'. When the metal is deformed\, the cluster of close neig
 hbours just shuffles around the central atom without breaking the cluster 
 bond.
LOCATION:TCM Seminar Room
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