We present a method for predicting the vibrational modes of small semiconductor clusters. We employ ab initio pseudopotentials and apply a higher-order finite difference procedure to solve the Kohn-Sham equations. We predict the vibrational modes of small silicon clusters (Sin, n = 4-7) based on their ground state structures. Our calculated vibrational modes agree very well with experimental data, and with other theoretical calculations based on quantum chemistry and tight binding methods. This comparison confirms the accuracy of the finite difference procedure for calculating not only the first order derivative of the energy, but the second derivatives as well. It also validates the accuracy of pseudopotential-local density calculations for the ground state structures for Si clusters.
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Acknowledgements - We would like to acknowledge the support for this work by the National Science Foundation, and by the Minnesota Supercomputer Institute.W e would like to thank Dr Nadia Bingelli for helpful discussions.
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