Sunday, 16 March 2014

Non-adiabatic dynamics with coupled-cluster and ADC

For non-adiabatic dynamics you could either be using CASSCF, which is a pain with respect to choosing the active space, or multireference CI, which is more reliable but also much more expensive. You could be computing approximate non-adiabatic interactions at the TDDFT level, which is much faster but carries all the problems of TDDFT. All these methods have their justifications (and are in fact available in Newton-X), but we wanted to open another route: coupled cluster (CC) and algebraic diagrammatic construction (ADC) dynamics, which we introduce in our new JCTC paper: "Surface Hopping Dynamics with Correlated Single-Reference Methods: 9H-Adenine as a Case Study".

CC2 and ADC(2) are available in a very efficient implementation in Turbomole. All we had to do is produce some approximate non-adiabatic coupling terms. Our "trick" was the following (in a similar spirit to what they do for TDDFT): take only the single excitation part of the response vector, construct a renormalized CIS vector out of this, and compute the wavefunction overlap of these vectors at two different timesteps. The first numerical tests were very promising and it looks like this can really be a viable method.

The limitation is that CC and ADC (just as TDDFT) are not able to describe intersections with the closed shell ground state correctly. But, if you are interested in non-adiabatic excited state processes ADC(2) may be the method of choice for you. According to some of our previous experience, potential applications include:
So, if you do have a Turbomole license, it definitly makes sense to check out the new methods.

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