Hello, My guess: you have to remove one of the imaginary frequencies (most probably the smallest one) by following the corresponding eigenvector (=moving the atoms accordingly). Then, you will have to make sure that the transition state connects the reactants and products you are interested in.
HTH, Pascal Pascal Boulet — Professor in computational chemistry - DEPARTEMENT OF CHEMISTRY Aix-Marseille University - ST JEROME - Avenue Escadrille Normandie Niemen - F-13013 Marseille - FRANCE Tél: +33(0)4 13 55 18 10 - Fax : +33(0)4 13 55 18 50 Site : http://madirel.univ-amu.fr/pages_web_BOULET_PASCAL/infos - Email : pascal.bou...@univ-amu.fr Le 13 nov. 2017 à 12:44, JAY Antoine <antoine....@isae-supaero.fr> a écrit : > Dear all, > I have been using NEB to obtain the Delta E and phonon DOS at > begining/end/saddle point to properly evaluate the vibrationnal entropy > contribution in the transition state theory. > Commonly, one frequency in "negative" at the saddle point, the one that is > "responssible" of the transition and the following of its eigen vector from > the initial state give the minimum energy path. > However, when two phonon frequencies are "negatives" at the saddle point, > that means that at least 3 energy minima are link together to the same > saddle point. > The transition state theory cannot be applied there as the preexponential > term is the ratio of the 3N-3 phonon frequencies of initial state over the > 3N-4 frequencies of the saddle point, giving the dimension of a time (state > life time) > Using 3N-5 frequencies without the two negatives ones would not have a > physical meaning for the initial partition function. > > Any idea on how to treat such a problem to evaluate the transition rate would > be appreciated. > > Best regards. > > Antoine Jay _______________________________________________ > Pw_forum mailing list > Pw_forum@pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum
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