We have carried out extensive LDA calculations to investigate the structures of small (AlP) N clusters. We find that the polarity of the Al-P bond has a significant effect on the cluster geometries and that the need to minimize electrostatic repulsion between relatively diffuse lone pair electrons on phosphorous atoms is a dominant energetic consideration in the structural arrangement. 36.40+d; 61.43.Bn; 61.46.+w; 68.35.Bs; 82.65.My As the drive towards miniaturization of electronic devices accelerates, there is a pressing need to investigate the properties of low-dimensional semiconductors [1]. For this reason, the past few years have witnessed enormous scientific activity in the experimental and theoretical investigations of semiconductor clusters of nanometer dimensions [2][3][4]. In this paper we examine evolution of (AlP) N cluster structures using density functional calculations and compare the results with the corresponding geometries of Si 2N clusters.
PACS:AlP and Si 2 are isoelectronic. In addition, bulk AlP and silicon have identical crystal structures and similar band structures [5]. Hence, a comparative study of the structures of (AlP) N and Si 2N clusters will yield insights into the factors governing growth and nucleation of silicon clusters. The differences between these two types of clusters will be informative on the effects of bond polarity on the energetics of atomic arrangement of heteroclusters in general. Such a study is also useful for an understanding of possible structural patterns that other IIIA-VB semiconductor clusters assume.Previous computational studies of alloy clusters were confined to small binary clusters by Raghavachari [6], Andreoni [7], Nordlander [8], and their respective co-workers. They have used ab initio quantum chemistry or density functional (DFT) techniques to investigate the electronic structure and geometries of AlP, MgS, and GaAs clusters. Their studies indicated that the ionicity of the heteropolar bond has a significant effect on the energetics of the cluster structures. More ionic clusters, such as MgS, prefer geometries with alternating electronegative and electropositive elements, as in NaCl clusters [6], while less ionic clusters, such as GaAs, assume Si N type geometries [6,7]. Since these studies were limited to very small clusters, it is difficult to descern a definitive trend in the evolution of cluster structures and relate that information to the electronegativity differences between constituent elements. Consequently, in this paper we examine the structures of AlP clusters in detail over a broader range of sizes.Our calculations employ the density functional theory (DFT) within the local density approximation (LDA) to evaluate the total energies of clusters [9,10]. Within this formal scheme, we employ the Car-Parrinello (CP) technique to optimize the electronic wavefunction as well as atomic positions [11][12][13][14]. The cluster is placed in a simple cubic unit cell of sidelength 20.0 a.u. and the exchange-correlation functional is evaluated on ...