Local bond order parameters for accurate determination of crystal structures in two and three dimensions

Local order parameters for the characterization of liquid and different two- and three-dimensional crystalline structures are presented. The order parameters are expressed in terms of the angular correlations between a vector (defined in terms of the spherical harmonics, identifying the local environment around a central particle) and its neighboring vectors. For the three-dimensional systems, we have undertaken simulation of the Lennard-Jones (12-6) particles and metallic systems at the melting temperature. The proposed order parameters are shown to accurately discriminate between liquid, fcc, hcp, and bcc phases. The simulated two-dimensional systems consist of liquid, Kagome, square, honeycomb, and hexagonal phases formed from a solution of triblock Janus colloidal particles, sedimented on the top of a supporting surface. The presented order parameters resolve all phases. A comparison was made between the predictive ability of the present order parameters and the popular three-dimensional [Lechner and Dellago, J. Chem. Phys., 2008, 129, 114707] and two-dimensional [Mermin, Phys. Rev., 1968, 176, 250] order parameters in the literature in the identification of crystal structures. In both cases, advancements in the present scheme, over the existing methods in the literature, are seen.