Geometrically active atomic states and the formation of molecules in their normal shapes

Nicolaides, CA; Komninos, Y

dc.contributor.author	Nicolaides, CA	en
dc.contributor.author	Komninos, Y	en
dc.date.accessioned	2014-03-01T01:47:13Z
dc.date.available	2014-03-01T01:47:13Z
dc.date.issued	1998	en
dc.identifier.issn	00207608	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/25175
dc.relation.uri	http://www.scopus.com/inward/record.url?eid=2-s2.0-0003752924&partnerID=40&md5=cc34a0be53a4a2bd98501d8085df43d6	en
dc.subject	Geometrically active atomic states	en
dc.subject	Molecular formation	en
dc.subject	Molecular shape	en
dc.subject	Shape of atomic states	en
dc.title	Geometrically active atomic states and the formation of molecules in their normal shapes	en
heal.type	journalArticle	en
heal.publicationDate	1998	en
heal.abstract	We present a theory of molecular formation according to which the shape of polyhedral or coordination compounds is fixed to a very good approximation by the shape of a particular state (or states) of the central atom, which is activated by spin and spacial coupling of optimal strength between this state, called the geometrically active atomic state (GAAS) and the state of the ligands. For a molecule with a central atom, spacial coupling of optimal strength, means that the shape of the GAAS fixes the position of the ligands according to the maximum overlap principle of the Heitler-London, Slater, and Pauling theory of covalent bonding, whereby much of the energy lowering from the free atom limit is obtained by the maximization of the contribution of the exchange integrals. Hence, a direct causal relationship between the shape of the GAAS and the shape of the molecular state at equilibrium seems to exist. This relationship implies a picture of diabatic connection between the geometrically asymptotic region and the equilibrium region, which is driven by the coupled GAAS and provides the ""why"" of molecular shape. Since the latter is fixed by the shape of the GAAS (in cases of electronic complexity or of molecular instability it is possible that more than one GAAS contribute simultaneously), prediction of the shape of certain large systems can be made based on the a priori recognition of the corresponding GAAS. The concept of the shape of atomic states defined and computed quantum mechanically from the probability distribution ρ(cos θ12) of the angle θ12 that the position vectors of two electrons form in the given atomic state. Specifically, it is deduced from the distribution's maxima which provide the most probable values of θ12. As shown previously [Y. Komninos and C. A. Nicolaides, Phys. Rev. A 50, 3782 (1994)], ρ(cos θ12) is obtainable directly from the state-specific expression for the Coulomb interaction, where the Rk integrals are replaced by Legendre polynomials Pk, multiplied by normalization constants and radial overlaps. The theory is demonstrated by explaining the shape of BeH2, BH2, CH4, SiH4, H2O, H2S, NH3, PH3, SF6, and TiH4 in terms of the shapes of the following GAAS. Be: 2s2p3P0, B: 2s2p24P, C: 2s2p35S0, Si: 3s3p3 S0, O: 2s2p53P0, S: 3s23p3d3P0 N: 2s2p44P, P: 3s3p33d4P0, S: 3s3p33d27F0, and Ti: 3d24s4p5G0. © 1998 John Wiley & Sons, Inc.	en
heal.journalName	International Journal of Quantum Chemistry	en
dc.identifier.volume	67	en
dc.identifier.issue	5	en
dc.identifier.spage	321	en
dc.identifier.epage	328	en