chemical bonding in solids from ab-initio calculations...
TRANSCRIPT
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Chemical bonding in solids from ab-initio calculations -I
24 March 2011; V172
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Transfer of electron from electropositive ion to the electronegative ion
Coulomb interactions plays an important role
Size of the cation reduces and size of anion increases
Electro-negativity difference between ions decide the strength of ionic bonding.
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Electrons moved from ions and distributed uniformly in the interstitial regions.
The electrons in the interstitial regions move freely around the crystal.
Good conductors and ductile
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Charge Density Distribution in TiC – Mixed iono-covalent bonding
Depleted Charge at Ti site indicate the electron transfer from Ti to C – ionic bonding
Finite charge in between atoms and their nonspherical distribiution show the covalent bonding.
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Charge transfer plot
Diamond (covalent)
Nb ( metallic)
NaCl (ionic)
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
AlP (polar)
eAl (metallic)
elf=0.5
NaCl (ionic)
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Charge density
Formation of molecularlike H-Ni-H (NiH2 ) sub units
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Charge transfer
(r)=(r)comp. - (r)atomic
Ionic bonding between H and the host lattice
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
ELFThe polarization of negative charges at H towards the electropositive La and In
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Charge density Charge transfer ELF
Ravindran et al. PRL (2002)
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Chemical bonding
Charge density Charge transfer ELF
KMgH3 – example for dominant ionic bonding
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Charge density Charge transfer ELF
La3+Sc3+O36-
It is not a perfect ionic material and has finite covalency
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Crystal structure of Ca3 Co2 O6
Rhombohedral (R-3c space group) with 22 atoms/unit cell
Alternating face-shared octahedra and trigonal prisms form one- dimensional chains along c-axis
Hexagonal with 66 atoms /unit cell
Co spins are arranged along c-axis
For every two-up spin chain, there is one down-spin chain resulting in Ferrimagnetic structure
One-dimensional Oxides
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Charge density and related features in Ca3 Co2 O6
Charge density Charge transfer ELF
Very weak interaction between Co1 and Co2
Magnitude of covalent interactions between Co1-O and Co2- O are different .
There is strong covalent interaction within the chain and ionic interaction between Ca and the chains.
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Bonding study from density of states analysis
Ca is in completely ionizedstate, donating almost all itsvalence electrons to O.
Co is in two different oxidation and/or spin states, seen from difference in the topology of DOS curves.
Oxygen is energetically degenerate with Co1 and Co2 forming strong covalent bond with them.
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Partial Density Of States in KGaH4
- Well separated Ga-s and -p state
- Energetically degenerated H-s and Ga-p states
- Strong covalent bonding Ga-H
- Ionic bonding between K and H
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Charge Density Distribution in KGaH4
0.2
0.15
0.1
0.05
0.001
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Lone pair electrons in BiMnO3
Seshadri and Hill, Chemistry of Materials, 13, 2892 (2001)
Visualization of lone pairFrom ELF
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
ELF isosurface (0.7) show that Bi lone-pair electrons are responsible for ferroelectricity.
Ravindran et al. PRB (2006)
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Chemical bonding in BiFeO3 from DOS analysis
Isolated Bi-s is the lone pair electrons.
Negligible Bi electrons in the valence band indicate ionic bonding
Degenerate Fe-d and O-p states indicate the covalent bonding.
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P.Ravindran, FME-course on Ab initio Modelling of solar cell Materials 24 February 2011 Chemical bonding in solids from abinitio calculations -I
Charge density Charge Transfer ELF