I am doing a simple scan of a water molecule and I am a little confused by the results I am getting. The forces and positions are as follows:
Tardis:water_bend_long matthew$ more water090_vmm.xyz
ITEM: TIMESTEP
0
ITEM: NUMBER OF ATOMS
3
ITEM: BOX BOUNDS pp pp pp
0 100
0 100
0 100
ITEM: ATOMS id type x y z ix iy iz fx fy fz
1 1 0 0 0 0 0 0 0 0.114476 0.114476
2 2 0 0 0.9578 0 0 0 0 6.11406 -0.114476
3 2 0 0.9578 0 0 0 0 0 -0.114476 6.11406
Tardis:water_bend_long matthew$ more water095_vmm.xyz
ITEM: TIMESTEP
0
ITEM: NUMBER OF ATOMS
3
ITEM: BOX BOUNDS pp pp pp
0 100
0 100
0 100
ITEM: ATOMS id type x y z ix iy iz fx fy fz
1 1 0 0 0 0 0 0 0 0.114039 0.104498
2 2 0 0 0.9578 0 0 0 0 4.08336 -0.114476
3 2 0 0.954155 99.9165 0 0 -1 0 0.241849 4.07779
However the pressure that is calculated for the first system is:-0.0050121063
and the second is: 32.230831
Now the second makes sense. I am forcing two hydrogens together so the pressure should rise as the angle gets smaller. The only thing I can think of is that it has something to do with the position of the atoms relative to the box corner but if this is the case then it is a real problem, that I have no idea how to fix. I’ve checked the forces and they are reasonable.
thanks all very much in advance
matthew