Effect of external drive on strongly coupled Yukawa systems: A nonequilibrium molecular dynamics study

Using nonequilibrium molecular dynamics (MD) simulations behavior of three-dimensional (3D) Yukawa system has been studied in the presence of a small amplitude drive along one direction (say z). This drive has the general form V=V-0 cos(k(L)z)Theta(t-t(0)), where Theta(t-t(0)) is a Heaviside step function in time at t=t(0) and k(L)=2 pi/L, L being the size of the system; V-0 is considered small compared to average interparticle potential energy. In particular, a 3D equilibrated Yukawa crystal (bcc) near solid-liquid transition is subjected to an external drive at times t >= t(0) at the largest possible scale. For a given k(L) it is observed that there exists a critical amplitude (V-0(c)) of the external drive below which the crystalline order is preserved and above which (V-0 >= V-0(c)) the transition from bcc to strongly coupled Yukawa liquid is observed. This critical amplitude (V-0(c)) is sensitive to the location of the Yukawa solid in the (kappa,Gamma) phase space. Various signatures of melting, transients, and steady state in the presence of this drive are elucidated using extensive MD diagnostics such as loss of long-range crystalline order, change in diffusion from subnormal to normal, and the fall of transversal shear peak in the Fourier transform of the velocity autocorrelation function. The mechanism of heating in the transient state is attributed to the local heating of the system where the forces are maximum. It is shown that these local hot regions dissipate heat into surrounding regions ultimately leading to a uniform temperature throughout the system. Ion streaming due to external field has been neglected.