By P. Schmelcher, L. S. Cederbaum, U. Kappes (auth.), E. S. Kryachko, J. L. Calais (eds.)

The rivers run into the ocean, but the ocean isn't really complete Ecclesiastes what's quantum chemistry? the easy resolution is that it's what quan­ tum chemists do. however it has to be admitted, that during distinction to physicists and chemists, "quantum chemists" appear to be a slightly ill-defined class of scientists. Quantum chemists are kind of physicists (basically theoreticians), roughly chemists, and through huge, computationists. yet initially, we, quantum chemists, are wakeful beings. We may perhaps adequately bet that quantum chemistry used to be one of many first components within the common sciences to lie at the obstacles of many disciplines. We may well definitely declare that quantum chemists have been the 1st to exploit desktops for quite huge scale calculations. The scope of the issues which quantum chemistry needs to reply to and which, via its specific nature, basically quantum chemistry can in basic terms resolution is growing to be day-by-day. Retrospectively we could bet that lots of these difficulties meet a regular desire, or are say, technical in a few experience. the remaining are basic or conceptual. The everyday life of such a lot quantum chemists is mostly packed with greedy the kind of technical difficulties. however it is no less than as very important to commit your time to the opposite type of difficulties whose resolution will open up new views for either quantum chemistry itself and for the average sciences in general.

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S. 7) can be neglected and the first and second term determine the sign of the second derivative of the energy with respect to 0. For states with a negative magnetic quantum number Ma< 0 we obtain for arbitrary field strengths and over a wide range of internuclear distances a positive second derivative. The electronic energy possesses then a local minimum at 0 =O. Only for very small internuclear distances and/or positive magnetic quantum numbers Ma this extremum changes to a local maximum. If the third term in eq.

18) is the usual assumption to derive the Born-Oppenheimer approximation in the absence of an external field. There exist now two possibilities to carry over conditions ofthe type ofeq. 18) to the case of the presence ofa magnetic field. The first possibility would be just to take over eq. 9) in the Born-Oppenheimer approximation. Within this approximation scheme the diagonal term of the nonadiabatic coupling elements contains the effect of the screening of the nuclear charges against the magnetic field and must, therefore, be 24 included in the nuclear equation of motion for a correct description of nuclear dynamics.

First of all we observe that the minima of the surfaces become more pronounced, i. e. the bond lengths decrease and the binding energy increases. Another important difference to the field-free case is the appearance of new additional vibrational degrees of freedom which lead to an increase of the dimension of the electronic potential surfaces. Let us consider as an example a diatomic molecule in a magnetic field. Its potential surfaces depend not only on the internuclear distance but also on the angle between the internuclear and magnetic field axis.

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