Extending to continuous potentials a cleaving wall molecular dynamics simulation method recently developed for the hard-sphere system ͓Phys. Rev. Lett. 85, 4751 ͑2000͔͒, we calculate the crystalmelt interfacial free energies, ␥, for a Lennard-Jones system as functions of both crystal orientation and temperature. At the triple point, T*ϭ0.617, the results are consistent with an earlier cleaving potential calculation by Broughton and Gilmer ͓J. Chem. Phys. 84, 5759 ͑1986͔͒, however, the greater precision of the current calculation allows us to accurately determine the anisotropy of ␥. From our data we find that, at all temperatures studied, ␥ 111 Ͻ␥ 110 Ͻ␥ 100 . A comparison is made to the results from our previous hard-sphere calculation and to recent results for Ni by Asta, Hoyt, and Karma ͓Phys. Rev. B 66 100101͑R͒ ͑2002͔͒.

We present a direct calculation by molecular-dynamics computer simulation of the crystal͞melt interfacial free energy g for a system of hard spheres of diameter s. The calculation is performed by thermodynamic integration along a reversible path defined by cleaving, using specially constructed movable hard-sphere walls, separate bulk crystal, and fluid systems, which are then merged to form an interface. We find the interfacial free energy to be slightly anisotropic with g 0.62 6 0.01, 0.64 6 0.01, and 0.58 6 0.01k B T ͞s 2 for the (100), (110), and (111) fcc crystal͞fluid interfaces, respectively. These values are consistent with earlier density functional calculations and recent experiments. 05.70.Np, 68.35.Md A detailed microscopic description of the interface between a crystal and its melt is necessary for a full understanding of such important phenomena as homogeneous nucleation and crystal growth [1][2][3]. Computer simulation studies of model materials have had some success in elucidating the phenomenology of such systems [4], the importance of such work being enhanced by the near absence of reliable experimental studies. These efforts, however, have been primarily focused on structural and dynamical properties, since the central thermodynamic property, the crystal͞melt interfacial free energy, is difficult to measure by simulation or experiment. In this Letter we report the results of a direct calculation via moleculardynamics (MD) simulation of the crystal͞melt surface free energy of the hard-sphere system, one of the most important reference models for simple materials.The crystal͞melt surface free energy g is defined as the (reversible) work required to form a unit area of interface between a crystal and its coexisting melt. Experimentally, g can be measured either indirectly from measurements of crystal nucleation rates interpreted through classical nucleation theory or directly by contact angle measurements [1]. Using the former method, Turnbull [5] estimated g for a number of materials and found a strong empirical correlation between the values obtained and the latent heat of fusion for each material given by the relation g ഠ C T D f Hr 2͞3 , where r is the number density of the crystal and with C T (the Turnbull coefficient) taking on the value 0.45 for most metals and 0.32 for other mostly nonmetallic materials. For the hard-sphere system considered in this Letter, recent experiments [6] of the crystallization kinetics of a colloidal suspension of coated silica spheres, which closely mimic hard spheres, have been interpreted within a classical nucleation model to yield an estimate for g of the hard-sphere system of ͑0.55 6 0.02͒k B T ͞s 2 [7]. This value is in agreement [8] with that predicted using the empirical relationship above assuming a C T of 0.45 and values of D f H and coexistence densities for hard spheres as determined by MD simulation [9]. Unfortunately, the accuracy of the values of g obtained from nucleation rates is severely limited by the approximations inherent in classical n...

We present a new method for isothermal rigid body simulations using the quaternion representation and Langevin dynamics. It can be combined with the traditional Langevin or gradient (Brownian) dynamics for the translational degrees of freedom to correctly sample the canonical distribution in a simulation of rigid molecules. We propose simple, quasisymplectic second-order numerical integrators and test their performance on the TIP4P model of water. We also investigate the optimal choice of thermostat parameters.

In this work, we examine in detail the structure and dynamics of the face-centered cubic ͑100͒ and ͑111͒ crystal-melt interfaces for systems consisting of approximately 10 4 hard spheres using molecular dynamics simulation. A detailed analysis of the data is performed to calculate density, pressure, and stress profiles ͑on both fine and coarse scales͒, as well as profiles for the diffusion and orientational ordering. The strong dependence of the coarse-grained profiles on the averaging procedure is discussed. Calculations of 2-D density contours in the planes perpendicular to the interface show that the transition from crystal to fluid occurs over a relatively narrow region ͑over only 2-3 crystal planes͒ and that these interfacial planes consist of coexisting crystal-and fluidlike domains that are quite mobile on the time scale of the simulation. We also observe the creation and propagation of vacancies into the bulk crystal.