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 {\textquoteleft}{\textquoteleft}number profile{\textquoteright}{\textquoteright} is compared with that expected from the partitioning of the 1D bond-distance into atom-specific transferable {\textquoteleft}{\textquoteleft}hub{\textquoteright}{\textquoteright} or core atomic sizes of the M and X atoms and another {\textquoteleft}{\textquoteleft}axle{\textquoteright}{\textquoteright} size which is associated with a pair of (bonding) electrons. The {\textquoteleft}{\textquoteleft}hub{\textquoteright}{\textquoteright} size is proportional to a core atom-specific size, r(nZ)(c) with r(nZ)(c)(M) \>= r(nZ)(c)(X). For {\textquoteleft}{\textquoteleft}single bonds{\textquoteright}{\textquoteright}, the {\textquoteleft}{\textquoteleft}hub{\textquoteright}{\textquoteright} size for M atom is C(M)r(nZ)(c)(M) and for X atom is C(X)r(nZ)(c)(X). The {\textquoteleft}{\textquoteleft}axle{\textquoteright}{\textquoteright} size, DMX, is usually the ordinary (similar to 4a(H)/3 where a(H) is the Bohr radius of the hydrogen atom) or elongated (similar to 2a(H)) bond length of the hydrogen molecule. The {\textquoteleft}{\textquoteleft}hub{\textquoteright}{\textquoteright} and {\textquoteleft}{\textquoteleft}axle{\textquoteright}{\textquoteright} sizes could be characterized {\textquoteleft}{\textquoteleft}charge-transfer{\textquoteright}{\textquoteright} (C(M) = pi(2/3) = 2.144; C(X) = pi(4/3)/2 = 2.300 and D(MX) = 4a(H)/3) or {\textquoteleft}{\textquoteleft}neutral{\textquoteright}{\textquoteright} (CM or C(X) = 1, 2, ... and D(MX) = 2a(H)). We use a new {\textquoteleft}{\textquoteleft}static{\textquoteright}{\textquoteright} or {\textquoteleft}{\textquoteleft}peripatetic{\textquoteright}{\textquoteright} classification for the core sizes which is derived from a new condition for metallization in elements based on atomic size. The charge-transfer distance, d(MX)(+/-), is usually found for {\textquoteleft}{\textquoteleft}static{\textquoteright}{\textquoteright} conditions while the {\textquoteleft}{\textquoteleft}neutral{\textquoteright}{\textquoteright} description is usually found when X = F or for {\textquoteleft}{\textquoteleft}peripatetic{\textquoteright}{\textquoteright} 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 Nel vs r plots from each atom are described by a simple hydrogen-atom-like function which differ away ({\textquoteright}{\textquoteright}out{\textquoteright}{\textquoteright}) or towards ({\textquoteright}{\textquoteright}in{\textquoteright}{\textquoteright}) the M-X bond. Thus N(in,out)(M, X) = (Z(M,X) +/- 1) exp (-r/B(in,out)) where the minus sign is associated with M and plus sign with X and Bin, out being related inversely to the Slater orbital exponent. (C) 2009 Elsevier B.V. All rights reserved.

}, keywords = {B3LYP, Bond length, Bond-stretch isomer, DFT, Diatomic molecule}, issn = {0022-2860}, doi = {10.1016/j.molstruc.2009.07.007}, author = {Ganguly, Parthasarathy and Kulkarni, Bhakti S. and Pal, Sourav} }