On the interpolation of the frequencies of vibrational modes in variational transition state calculations: An adiabatic or diabatic scheme?

The convenience of a diabatic or an adiabatic interpolation of frequencies in variational transition state calculations involving interpolation methodologies is discussed. The gas phase proton transfer between butanone and a hydroxide anion has been used to illustrate the theoretical discussion. For example, it has been shown that if vibrational normal mode crossings exist the simple adiabatic interpolation can produce incorrect entropy contributions and, as a consequence, a spurious displacement of the generalized transition state. © 1996 Taylor & Francis Group, LLC.