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Bond length variations: Electron number profiles and transferable atomic sizes
- Source :
-
Journal of Molecular Structure . Nov2009, Vol. 936 Issue 1-3, p1-8. 8p. - Publication Year :
- 2009
-
Abstract
- Abstract: A profile of the number of electrons with distance along the M–X bond in gas-phase diatomic molecules has been obtained from electron density plots calculated using DFT B3LYP 6-311G∗∗ method for some representative molecules. This “number profile” is compared with that expected from the partitioning of the 1D bond-distance into atom-specific transferable “hub” or core atomic sizes of the M and X atoms and another “axle” size which is associated with a pair of (bonding) electrons. The “hub” size is proportional to a core atom-specific size, rnZ c with rnZ c (M)⩾ rnZ c (X). For “single bonds”, the “hub” size for M atom is CMrnZ c (M) and for X atom is CXrnZ c (X). The “axle” size, DMX , is usually the ordinary (∼4aH /3 where aH is the Bohr radius of the hydrogen atom) or elongated (∼2aH ) bond length of the hydrogen molecule. The “hub” and “axle” sizes could be characterized “charge-transfer” (CM =π2/3 =2.144; CX =π4/3/2=2.300 and DMX = 4aH /3) or “neutral” (CM or CX =1, 2, … and DMX =2aH ). We use a new “static” or “peripatetic” classification for the core sizes which is derived from a new condition for metallization in elements based on atomic size. The charge-transfer distance, dMX ±, is usually found for “static” conditions while the “neutral” description is usually found when X=F or for “peripatetic” conditions. Such a partitioning is seen to agree with that from the plot of the total number of electrons, N el, vs r along a bond axis. The N el vs r plots from each atom are described by a simple hydrogen-atom-like function which differ away (“out”) or towards (“in”) the M–X bond. Thus N in,out(M,X)=(ZM,X ±1)exp(−r/B in,out) where the minus sign is associated with M and plus sign with X and B in,out being related inversely to the Slater orbital exponent. [Copyright &y& Elsevier]
Details
- Language :
- English
- ISSN :
- 00222860
- Volume :
- 936
- Issue :
- 1-3
- Database :
- Academic Search Index
- Journal :
- Journal of Molecular Structure
- Publication Type :
- Academic Journal
- Accession number :
- 44263171
- Full Text :
- https://doi.org/10.1016/j.molstruc.2009.07.007