Using a newly developed gold Embedded Atom Model potential we conducted molecular dynamics simulations of inert gas aggregation type nanoparticle growth to investigate morphology transformations during the growth process. Our simulations reveal a size and temperature dependent mechanism whereby nanoparticles of Marks decahedron (m-D-h) morphology are transformed to icosahedron (I-h) nanoparticles via a solid-state process. The findings provide a theoretical explanation for recent experimental population statistics of gold nanoparticles produced by inert gas aggregation methods and may assist in developing methods for producing highly uniform nanoparticle morphologies. (C) 2009 Elsevier B. V. All rights reserved.