Simulation study of Al3+ coordination in NaF-AlF3 mixtures: development ofinteraction potentials

The generation of suitable interaction potentials with which to study the c oordination chemistry of Al3+ ions in NaxAlF3+x mixtures by computer simula tion is described. The potentials reflect an 'extended ionic' model of the interactions in this system, with formal ionic charges and many-body polari zation effects included. The parameters are derived from a mixture of ab in itio and empirical information. For the Al-F interactions, the structure an d energetics of crystalline and molecular AlF3 form the database. This pote ntial is then combined with an NaF potential and used to predict the crysta l structures of three NaxAlF3+x crystalline compounds and also the vibratio nal frequencies of the NaAlF4 molecule, which have been obtained experiment ally. Excellent agreement is found. The potentials will be used in simulati ons of the spectroscopic and structural properties of Na(x)AIF(3+x) melts.