Calcium phosphate clusters

The potential energy surfaces associated with [Ca-3(PO4)(2)](n) clusters ar e analyzed in detail using ab initio calculations for n ranging from one to four. Considering separated clusters, energy criteria favor the so-called Posner's cluster Ca-9(PO4)(6), which is the core of the actual structural m odel of amorphous calcium phosphate. This is rationalized through the exist ence of a distinct CaO bonding pattern in this cluster. Considering aggrega ted clusters as a possible model for amorphous calcium phosphate, the aggre gation of Ca-3(PO4)(2) clusters appears as an alternative to Posner's hypot hesis. (C) 2001 Elsevier Science Ltd. All rights reserved.