Cooke, David J. and Elliott, James A. (2009) Atomistic simulation of the crystallisation and growth of calcium carbonate nano-particles. Geochimica et Cosmochimica Acta, 73 (13, Su). A241. ISSN 0046-564X

Atomistic simulation of nano-particles is important
because it allows the size and shape-dependence of their
structure and thermodynamic properties to be studied directly.

In this paper we report on four broad areas of work modelling
the stability, aggregation and nucleation of CaCO3 nanoparticles.

We have simulated nano-particles of sizes ranging from 18
to 324 formula units, in vacuum and in water, from which
it is clear that the breakdown of structural order in the smaller
particles is caused by the rotation of CO3
2- groups on the
surface when there is little bulk mineral to stabilise the
structure. When water is present, the surface ions bond to the
water in the first hydration layer and thus are prevented from
rotating to the same extent. The structure of the water close to
the particle is strikingly similar to that previously seen when
considering infinite planer surfaces.

In an attempt to extend this initial work we have begun to
consider how such nano-particles aggregate to form macrosized
particles. Initially we have considered eight particles
consisting of 75CaCO3
units, both in vaccuo and in solution,
using a combination of potential of mean force and
conventional molecular dynamics. Initial results suggest that if
one face each particle is doped with Mg2+ the particles
aggregate so as to maximise the amount of Mg2+ on the
surface of the resulting combined particle.

At the other end of the scale it is also poddible to use
molecular dynamics to investigate the processes of cluster
formation and growth of CaCO3 from aqueous solution.

The influence of both temperature and concentration have
been studied and, using a combination of order parameters we
can relate the clusters that form to the structure of the larger
nano particles, considered in our earler work.

Finally we have begun to use meta-dynamic methods to
study these systems over longer time-scales than can be
accessed via standard simulation methodologies.

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