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SUMMARY:Understanding the Peculiarities of Metallic Bonding - Prof. Volker
  Heine FRS
DTSTART:20201111T113000Z
DTEND:20201111T123000Z
UID:TALK153220@talks.cam.ac.uk
CONTACT:Angela Harper
DESCRIPTION:The inter-atomic bonds in metals are basically (I) strong cova
 lent bonds\, but (II) metals are malleable and ductile\, with the bonding 
 structure re-arranging relatively easily. Also (III) metals tend to be goo
 d catalysts\, and (IV) the formation energy of an atomic vacancy or a surf
 ace is only about half of what one might expect from counting the net numb
 er of bonds broken.\n\nAll four properties are explained by a simple model
 \, but treated rigorously quantum mechanically\, for a band of one type of
  electron (e.g. atomic s-electrons or five d-electrons). Then the bonding 
 per electron is approximately proportional to the r.m.s. (root mean square
 ) energy band width W of the electron distribution.\n\nA simple quantum me
 chanical calculation shows that W is proportional to the *square root* of 
 the number z of nearest neighbours\, which then gives properties II to IV.
 \n\nParallels can be seen in traditional chemistry\, including graphite be
 ing more stable than diamond (re I above). Unsaturated ring structures suc
 h as benzene are stabilised by 'resonance' combination of many different b
 onding patterns (re II) and the ubiquity of such ring structures throughou
 t biochemistry parallels points II\, III and IV.\n\nApplication to compute
 r modelling of defects in metals will be mentioned: also some ab initio ca
 lculations on 18 real and artificial structures of aluminium ranging from 
 the free atom (z=0) and di-atomic molecule (z=1) to z=12 (face centred cub
 ic). These (surprisingly) also follow quite well the square root form\, al
 though aluminium is a Nearly Free Electron gas of predominantly hybridised
  3s and 3p bonding. The crux seems to be that the square root function cur
 ves towards the axis\, whereas z-squared and even the linear function z ve
 er away from it.\n\nJoin Zoom Meeting:\n* https://bham-ac-uk.zoom.us/j/857
 02415099?pwd=VTh5aFZ4Sm9Nc1dxZXYwelJpc1JtZz09\n* Meeting ID: 857 0241 5099
 \n* Passcode: 501623\n
LOCATION:Zoom
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