[DFTB-Plus-User] Slow Convergence problem

[bikash sankar kanungo]

Hi,

Hi I am trying to relax an epoxy polymer matrix in DFTB . The polymer
matrix is obtained by cross-linking the epoxy monomers with a curing agent.
The cross-linking is done using Classical MD tool LAMMPS. Before feeding
the cross-linked structure(of 1322 atoms) from LAMMPS to DFTB I ensured to
keep the pressure to be 1 atm by doing NPT runs in LAMMPS. But while doing
structure relaxation in DFTB using Conjugate Gradient Driver I do not see
any change in order of magnitude of pressure which remains as high as
1.0E+09 Pa. With a hope of reducing the pressure to 1.0E05(1 atm) I even
tried Verlocity Verlet using Berendsen Thermostat and Barostat with target
temperature = 10K , target pressure=1.0E+05 Pa , Timestep=0.1fs, Timescale
= 50fs but the pressure still remains at around 1.0E+09 Pa even after 10fs.
To obtain SCC convergence I have set Broyden mixing parameter =
0.3(default=0.2\0 and Fermi Fillinf temperature=300K(default=0K). Do I need
to provide more time for convergence for such a large system or are there
other alternatives to boost the convergence rate?

I would appreciate any help or suggestions regarding the relaxation of this
seemingly difficult structure.

Thank you,
Bikash
-- 
BIKASH SANKAR KANUNGO
Final Year Undergraduate student,
Mechanical Engineering Department,
INDIAN INSTITUTE OF TECHNOLOGY
KHARAGPUR.
+919749935409
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.zfn.uni-bremen.de/pipermail/dftb-plus-user/attachments/20120816/99150547/attachment.htm>