Diabatic potential

To see physically the problem of motion of wavepackets in a non-diagonal diabatic potential, we plot in figure B3.4.17 a set of two adiabatic potentials and their diabatic counterparts for a ID problem, for example, vibrations in a diatom (as in metal-metal complexes). As figure B3.4.17 shows, if a wavepacket is started away from the crossing point, it would slide towards this crossing point (where where it would... 

The simplest approach to simulating non-adiabatic dynamics is by surface hopping [175. 176]. In its simplest fomi, the approach is as follows. One carries out classical simulations of the nuclear motion on a specific adiabatic electronic state (ground or excited) and at any given instant checks whether the diabatic potential associated with that electronic state is mtersectmg the diabatic potential on another electronic state. If it is, then a decision is made as to whedier a jump to the other adiabatic electronic state should be perfomied. 

In this section, we prove that the non-adiabatic matiices have to be quantized ( similar to Bohr-Sommerfeld quantization of the angulai momentum) in order to yield a continous, uniquely defined, diabatic potential matrix W(i). In another way, the extended BO approximation will be applied only to those cases that fulfill these quantization rules. The ADT matrix A(s,so) transforms a given adiabatic potential matiix u(i) to a diabatic matiix W(s, so)... 

However, in order to obtain a uniquely defined diabatic potential matrix, it is not necessary for the A matiix to be uniquely defined throughout CS. Still, we ignore this difficulty and go ahead to derive A by a direct integration of Eq. (62),... 

In a different field, location, and characteristics of ci s on diabatic potential surfaces have been recognized as essential for the evaluation of dynamic parameters, like non-adiabatic coupling terms, needed for the dynamic and... 

For a two-state system, the eigenfunctions of the diabatic potential matrix of Eq. (63) in terms of its elements are... 

In Section III.D, we shall investigate when this happens. For the moment, imagine that we are at a point of degeneracy. To find out the topology of the adiabatic PES around this point, the diabatic potential matrix elements can be expressed by a hrst order Taylor expansion. 

The potential matrix elements are then obtained by making Taylor expansions around 00, using suitable zero-order diabatic potential energy functions,... 

For diabatic calculations, the equivalent expression uses the diabatic potential matrix elements [218]. When the value of this coupling becomes greater than a pre-defined cutoff, the tiajectory has entered a non-adiabatic region. The propagation is continued from this time, ti, until the trajectoiy moves out of the region at time f2-... 

H3 (and its isotopomers) and the alkali metal triiners (denoted generally for the homonuclears by X3, where X is an atom) are typical Jahn-Teller systems where the two lowest adiabatic potential energy surfaces conically intersect. Since such manifolds of electronic states have recently been discussed [60] in some detail, we review in this section only the diabatic representation of such surfaces and their major topographical details. The relevant 2x2 diabatic potential matrix W assumes the fomi... 

A. The Necessary Conditions for Obtaining Single-Valued Diabatic Potentials and the Introduction of the Topological Matrix... 

The Adiabatic-to-Diabatic Transformation Matrix and the Diabatic Potentials... 

With these definitions we can now look for the necessary condition(s). Thus, we assume that at each point sq iu configuration space the diabatic potential matrix W(/l) [= W(s,so)] fulfills the condition ... 

In Section IV.A, the adiabatic-to-diabatic transformation matrix as well as the diabatic potentials were derived for the relevant sub-space without running into theoretical conflicts. In other words, the conditions in Eqs. (10) led to a.finite sub-Hilbert space which, for all practical purposes, behaves like a full (infinite) Hilbert space. However it is inconceivable that such strict conditions as presented in Eq. (10) are fulfilled for real molecular systems. Thus the question is to what extent the results of the present approach, namely, the adiabatic-to-diabatic transformation matrix, the curl equation, and first and foremost, the diabatic potentials, are affected if the conditions in Eq. (10) are replaced by more realistic ones This subject will be treated next. 

Thus, we still relate to the same sub-space but it is now defined for P-states that are weakly coupled to <2"States. We shall prove the following lemma. If the interaction between any P- and Q-state measures like 0(e), the resultant P-diabatic potentials, the P-adiabatic-to-diabatic bansfomiation maOix elements and the P-curl t equation are all fulfilled up to 0(s ). 

Once there is an estimate for the error in calculating the adiabatic-to-diabatic tiansfomiation matrix it is possible to estimate the error in calculating the diabatic potentials. For this purpose, we apply Eq. (22). It is seen that the error is of the second order in , namely, of 0( ), just like for the adiabatic-to-diabatic transformation matrix. 

XI. THE NECESSARY CONDITIONS FOR A RIGOROUS MINIMAL DIABATIC POTENTIAL MATRIX... 

For example one forms, within a two-dimensional (2D) sub-Hilbert space, a 2x2 diabatic potential matrix, which is not single valued. This implies that the 2D transformation matrix yields an invalid diabatization and therefore the required dimension of the transformation matrix has to be at least three. The same applies to the size of the sub-Hilbert space, which also has to be at least three. In this section, we intend to discuss this type of problems. It also leads us to term the conditions for reaching the minimal relevant sub-Hilbert space as the necessary conditions for diabatization. ... 

In this section, diabatization is formed employing the adiabatic-to-diabatic transformation matrix A, which is a solution of Eq. (19). Once A is calculated, the diabatic potential matiix W is obtained from Eq. (22). Thus Eqs. (19) and (22) form the basis for the procedure to obtain the diabatic potential matrix elements. 

We consider a 2D diabatic framework that is characterized by an angle, P(i), associated with the orthogonal transformation that diagonalizes the diabatic potential matrix. Thus, if V is the diabatic potential matrix and if u is the adiabatic one, the two are related by the orthogonal transformation matrix A [34] ... 

We consider a case where in the vicinity of a point of degeneracy between two electronic states the diabatic potentials behave linearly as a function of the coordinates in the following way [16-21]... 

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