Octobor 17 2002
Cooling of 201 and 603 atoms respectively
Both carved-out sphere systems went through constant temperature MD at
1000K. A million steps (4.3ns) for 201 atoms and half a million (2.15ns)
for 603 atoms. After that, the systems went through Andersen Thermostat
with the sampling rate of 0.01*dt. The systems were equilibrated at a certain
temperature level for a certain time, then cooled down to a lower temperature
level. The temperature levels of 1000K, 900K, 800K, 700K, 600K, 500K, 400K,
300K, 200K and 100K were performed. At each temperature level, the system
of 201 atoms was equilibrated for ten million steps (43ns) and that of
603 atoms was five million steps (21.5ns).
Parallel tempering of 201 atoms
The same Andersen thermostat program was modified to run parallel with
parallel tempering algorithm. The system configurations at different temperature
levels were trying to swap the configurations according to the swapping
rule of
acc(o->n) = min ( 1, exp[(1/kTi - 1/kTj)
* (ui - uj)] )
Where T is the system temperature and u is the system total potential energy.
For the system of 201 atoms, ten million steps (43ns) were perfromed
for the temperature levels of 200K, 233K, 267K, 300K, 350K, 400K, 450K,
500K, 550K, 600K, 650K, 700K, 750K, 800K, 900K and 1000K. The initial configurations
were taken from the results of cooling. The acceptance probabilites of
swapping were:
|
temperature levels
|
acceptance probabilities (%)
|
|
200K -- 233K
|
3.776
|
|
233K -- 267K
|
6.562
|
|
267K -- 300K
|
12.366
|
|
300K -- 350K
|
4.376
|
|
350K -- 400K
|
5.599
|
|
400K -- 450K
|
8.808
|
|
450K -- 500K
|
10.205
|
|
500K -- 550K
|
12.376
|
|
550K -- 600K
|
15.682
|
|
600K -- 650K
|
19.319
|
|
650K -- 700K
|
22.879
|
|
700K -- 750K
|
27.279
|
|
750K -- 800K
|
32.425
|
|
800K -- 900K
|
9.648
|
|
900K -- 1000K
|
12.881
|
The positions of the initial configurations were also tracked. The tracks
of the initial configurations of 200K and 500K are shown as examples:
The picture shows that the configurations were really brought up and
down the temperature levels.