The origin of the electron distribution in SnO

Gradient corrected density functional theory calculations have been perform ed on SnO in the litharge and idealized CsCl structures with the litharge s tructure in good agreement with experiment. The CsCl structured SnO has a s pherical electron density whereas the litharge structured SnO has a nonsphe rical electron distribution. Such asymmetry is often attributed to a steric ally active lone pair formed by the 5s(2) electrons which does not take par t in chemical bonding. However, analysis of the density of states and band structures indicates that the situation is more complicated. In CsCl struct ured SnO mixing of the Sn 5s with the oxygen 2p electronic states results i n filled bonding and antibonding combinations. The antibonding combinations , at the top of valence band, can interact with Sn 5p to stabilize the stru cture, only when in the distorted litharge structure resulting in the asymm etric electron density. This is in contrast to the classical theory of hybr idization of the tin 5s and 5p orbitals to form a "lone pair" as the asymme tric electron distribution is the result of the tin-oxygen covalent interac tions. (C) 2001 American Institute of Physics.