10,034 research outputs found
Stable and Efficient Linear Scaling First-Principles Molecular Dynamics for 10,000+ atoms
The recent progress of linear-scaling or O(N) methods in the density
functional theory (DFT) is remarkable. We expect that first-principles
molecular dynamics (FPMD) simulations based on DFT can now treat more realistic
and complex systems using the O(N) technique. However, very few examples of
O(N) FPMD simulations exist so far and the information for the accuracy or
reliability of the simulations is very limited. In this paper, we show that
efficient and robust O(N) FPMD simulations are now possible by the combination
of the extended Lagrangian Born-Oppenheimer molecular dynamics method, which
was recently proposed by Niklasson et al (Phys. Rev. Lett. 100, 123004 (2008)),
and the density matrix method as an O(N) technique. Using our linear-scaling
DFT code Conquest, we investigate the reliable calculation conditions for the
accurate O(N) FPMD and demonstrate that we are now able to do actual and
reliable self-consistent FPMD simulation of a very large system containing
32,768 atoms.Comment: 26 pages, 10 figures, accepted by J. Chem. Theory Compu
Supercooled Liquids Under Shear: Theory and Simulation
We analyze the behavior of supercooled fluids under shear both theoretically
and numerically. Theoretically, we generalize the mode-coupling theory of
supercooled fluids to systems under stationary shear flow. Our starting point
is the set of generalized fluctuating hydrodynamic equations with a convection
term. A nonlinear integro-differential equation for the intermediate scattering
function is constructed. This theory is applied to a two-dimensional colloidal
suspension. The shear rate dependence of the intermediate scattering function
and the shear viscosity is analyzed. We have also performed extensive numerical
simulations of a two-dimensional binary liquid with soft-core interactions
near, but above, the glass transition temperature. Both theoretical and
numerical results show: (i) A drastic reduction of the structural relaxation
time and the shear viscosity due to shear. Both the structural relaxation time
and the viscosity decrease as with an exponent , where is the shear rate. (ii) Almost isotropic dynamics
regardless of the strength of the anisotropic shear flow.Comment: 14 pages, 14 figure
Supercooled liquids under shear: A mode-coupling theory approach
We generalize the mode-coupling theory of supercooled fluids to systems under
stationary shear flow. Our starting point is the generalized fluctuating
hydrodynamic equations with a convection term. The method is applied to a two
dimensional colloidal suspension. The shear rate dependence of the intermediate
scattering function and shear viscosity is analyzed. The results show a drastic
reduction of the structural relaxation time due to shear and strong shear
thinning behavior of the viscosity which are in qualitative agreement with
recent simulations. The microscopic theory with minimal assumptions can explain
the behavior far beyond the linear response regime.Comment: 4 pages, 2 figures, Proceedings to Slow Dynamics in Complex Systems
November3-8, 2003 -- Sendai, Japa
Supercooled Liquids under Shear: Computational Approach
We have performed molecular dynamics simulations for a model two-dimensional
soft-core mixture in a supercooled state. The mixture exhibits a slow
structural relaxation in a quiescent state, however, the relaxation is much
enhanced in sheared states. There observed surprisingly small anisotropy both
in the coherent and incoherent density correlation functions even under
extremely strong shear which is times faster than the structural
relaxation rate. The present simulation results agree well with predictions of
the recently developed mode-coupling theory in shear.Comment: 2 pages, 2 figure
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