Branching space dimension, conical

We want to point out that the CHD model outlined in Sec. 3 is not a truly two-dimensional case. Instead, it is a 36 dimensional problem projected onto two dimensions which do not coincide with the diabatic branching space of the conical intersections. For this reason, it remains unclear whether to expect a phase jump or not. 

In these last equations, g = <5 is the gradient difference vector and h = A is the linear derivative coupling vector. The space spanned by these two vectors is called the - ft space or branching space whereas the space orthogonal to the branching space is the intersection space, also called conical intersection seam. Thus, a conical intersection is a subspace of the nuclear configuration space of dimension 3N-8, where N denotes the number of atoms of the system (the space of the nuclear configurations is of dimension 3N-6). 

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