| 1. |
- Davis, Sergio, et al.
(författare)
-
Model for diffusion at the microcanonical superheating limit from atomistic computer simulations
- 2011
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:6, s. 064102-
-
Tidskriftsartikel (refereegranskat)abstract
- The diffusion statistics of atoms in a crystal close to the critical superheating temperature was studied in detail using molecular dynamics and Monte Carlo simulations. We present a continuous random-walk model for diffusion of atoms hopping through thermal vacancies. The results obtained from our model suggest that the limit of superheating is precisely the temperature for which dynamic percolation happens at the time scale of a single individual jump. A possible connection between the critical superheating limit and the maximization of the Shannon entropy associated with the distribution of jumps is suggested. As a practical application of our results, we show that an extrapolation of the critical superheating temperature (and therefore an estimation of the melting point) can be performed using only the dynamical properties of the solid state.
|
|
| 2. |
- Davis, Sergio, et al.
(författare)
-
Molecular dynamics simulation of zirconia melting
- 2010
-
Ingår i: Central European Journal of Physics. - : Walter de Gruyter GmbH. - 1895-1082 .- 1644-3608. ; 8:5, s. 789-797
-
Tidskriftsartikel (refereegranskat)abstract
- The melting point for the tetragonal and cubic phases of zirconia (ZrO2) was computed using Z-method microcanonical molecular dynamics simulations for two different interaction models: the empirical Lewis-Catlow potential versus the relatively new reactive force field (ReaxFF) model. While both models reproduce the stability of the cubic phase over the tetragonal phase at high temperatures, ReaxFF also gives approximately the correct melting point, around 2900 K, whereas the Lewis-Catlow estimate is above 6000 K.
|
|
| 3. |
- Davis, Sergio, et al.
(författare)
-
SearchFill : A stochastic optimization code for detecting atomic vacancies in crystalline and non-crystalline systems
- 2011
-
Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 182:5, s. 1105-1110
-
Tidskriftsartikel (refereegranskat)abstract
- We present an implementation of a stochastic optimization algorithm applied to location of atomic vacancies. Our method labels an empty point in space as a vacancy site, if the total spatial overlap of a "virtual sphere", centered around the point, with the surrounding atoms (and other vacancies) falls below a tolerance parameter. A Metropolis-like algorithm displaces the vacancies randomly, using an "overlap temperature" parameter to allow for acceptance of moves into regions with higher overlap, thus avoiding local minima. Once the algorithm has targeted a point with low overlap, the overlap temperature is decreased, and the method works as a steepest descent optimization. Our method, with only two free parameters, is able to detect the correct number and coordinates of vacancies in a wide spectrum of condensed-matter systems, from crystals to amorphous solids, in fact in any given set of atomic coordinates, without any need of comparison with a reference initial structure.
|
|
| 4. |
- Loyola, C., et al.
(författare)
-
Onset of failure in argon by the effect of a shockwave : A molecular dynamics study
- 2010
-
Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 49:3, s. 582-587
-
Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamic simulations of shockwaves in solid argon were performed. The simulation cell contains 51,840 atoms at 5 K interacting by means of a pairwise potential. The shockwave itself was introduced explicitly in the simulation by a piston hitting the sample from one side of the simulation box, at speeds ranging from 1.2 to 1.3 times the speed of sound in solid argon at the chosen density. In order to characterize the sample in terms of both structural and dynamic properties, we determine the density and temperature profiles according the advance of the shockwave, evaluating, for different slabs, the pair-distribution function, coordination number as well as performing a common neighbor analysis for the atoms. Our simulations reproduce the experimental Hugoniot curve and show how the material is break due to rarefaction waves. The picture that emerges is that when the shockwave starts, a local melting is produced in a region of the sample. Then, as the shockwave travels through the sample, a high density disordered phase is identified. When the piston stops, a rarefaction wave develops, producing a large tensile stress, which finally causes the failure of the sample.
|
|
