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*Ab initio* Total Energy Studies of Minerals Using Density Functional Theory and the Local Density Approximation

Björn Winkler, Victor Milman and Michael C. Payne

Mineralogisch-Petrographisches Institut der Christian-Albrechts Universität, Olshausenstr. 40, D 24098 Kiel 1, Germany

Molecular Simulations, 240/250 The Quomm, Barnwell Road, Cambridge CB5 8RE, UK

Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK

**Abstract:** *Ab initio* total energy calculations based on the local density approximation (LDA) and using a conjugate-gradient solver for the Kohn-Sham equations have been performed for cordierite, brucite, (Mg(OH)_{2}) and diaspore (AlOOH). The calculated fractional coordinates of all structures are in good agreement with experimental diffraction data. The angle of the non-linear hydrogen bond in diaspore is reproduced well. The Raman active OH stretching frequency in brucite has been calculated using the frozen phonon approach and the calculated stretching frequency is in very good agreement with the observed value. The energetically most favourable calculated orientation of the proton-proton vector of an H_{2}O molecule incorporated in the structural channels of cordierite agrees with findings deduced from spectroscopic data, and the calculated energy of hydration is in reasonable agreement with calorimetric data. It is therefore concluded that *ab initio* total energy calculations can confidently be used to predict properties of hydrogen bonded structures, which is difficult with conventional parameterized static lattice energy minimization calculations. An extension to the model is necessary to improve the agreement of the predicted to the observed lattice parameters for small structures.