On diabatization and the topological D-matrix:: Theory and numerical studies of the H+H2 system and the C2H2 molecule

This article is divided into two main parts: ( 1) The theoretical part contains a new derivation of the topological matrix D ( M. Baer and A. Alijah, Chem. Phys. Lett., 2000, 319, 489) which is based, solely, on the spatial dependent electronic manifold. This derivation enables more intimate relations between the adiabatic and the diabatic frameworks as is discussed in detail in the manuscript. ( 2) The numerical part is also divided into two parts: ( a) In the first part we extend our previous study on the H+H-2 system ( G. Halasz, A. Vibok, A. M. Mebel and M. Baer, J. Chem. Phys., 2003, 118, 3052) by calculating the topological matrix for five states ( instead of three) and for configuration spaces four times larger than before. These studies are expected to yield detailed information on the possibility of diabatization of this system. (b) We report on preliminary results concerning the C2H2 molecule. So far we established the existence of one ( 1,2) conical intersection and we have good reasons to believe that this system contains several ( 2,3) and ( 3,4) conical intersections as well.