Sent to CCL by: "David Santos Carballal"
[spectrum_dav[*]operamail.com]
Dear CCl members:
I am doing some molecular dynamics in TINKER.
I made a box of solvent (water) with the program xyzedit.
In the keyword file evoke keywords: rattle (the responsible of shake method in
order to restrain O-H distances and angles in water); a-axis (to define lattice
lenght); octahedron (to simulate a sistem closer to a sphere) and cutoff (to
evaluate the integrals in a region smaller than the half of dimension of the box
of solvent).
My system have 100 water molecules.
First of all I made a minimization with a conjugate gradient of 0.01. After it I
run dynamic with the Beeman integration method and constant temperature (298K)
and pressure (1 atm.). When the dynamic begins temperature stabilizes so fast
but pressure is very high, it wuold be around 4000 atm. The pressure fall down
at 1 atm. after 12000 steps, but the lattice length grow up so much, the initial
lattice length was 14 angstroms and the final is 200 angstroms, with one
consecuence: density fall down until 0.0010 grams/cc, that is desagree with
water density. I use MM3 force field.
My question is I am using correctly periodic boundary conditions?
Why this results?