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COUPLED CLUSTER THEORY |
We have (long ago !) developed a time dependent version of the coupled cluster theory (CCT). The paper referred to below is one of the first applications for CCT to a genuinely time dependent problem. The problem involves the neutralization of an ion which is scattered from the surface of a metal was studied using a time dependent version of the Newns-Anderson Hamiltonian. The procedure consists of solving for the matrix elements of the time evolution operator explicitly. Including coulombic repulsions make the problem a difficult many body one. For ions with closed shells one can get time dependent Hartree-Fock solutions. It was shown that this solution is defective in that it predicts the probability of neutralization to be less than 0.5. This means that correlation effects have to be included for a correct description of the process. In order to account for correlation effects, a time dependent version of the coupled cluster theory was used. Using this, neutralization probabilities for Li+ ions scattered from the surface of Ni was calculated. Also the spectrum of excitations produced in the solid by the reflected ions have been calculated. This was one of the first development and application of time dependent coupled cluster to a genuinely time dependent problem.