Monte Carlo exploration

and Parallel Tempering Monte Carlo exploration

A

Get the MOLECULES file and create the following deMon.inp :
MONTECARLO MAX=10000 WALL=6
MCTEMP TMC=300 OUT=1
DFTB SCC DISP
PARAM PTYPE=MAT
/usr/local/deMonNano/basis
QUATERNION NMOL=3 RIGID
1 1.0 0.0 .0 1.0 0.0 0.0 0.0
2 0. -3. 0.0 0.7 0.7 0. 0.0
3 1. -3. -4.0 1.0 0.0 0.0 0.0
MOLECULES NMOL=3
1 WAT
2 WAT
3 WAT

Try to understand the MOLECULES and deMon.inp files, run the code and visualize the outputs (deMon.out and deMon.01.mol).

B

Perform a parallel tempering Monte Carlo exploration with 10 trajectories following a geometric evolution for the temperature distribution. Exchanges are tested each 20 steps

→ MCTEMP GEOM NTEMP=10 TEMPMIN=40 SMOD=20 TEMPMAX=300

Visualize the different trajectories
 →  molden deMon.04.mol ...
 →  molden deMon.10.mol ...
Put SDBG as a subkeyword of MCTEMP , it creates a debug_swap file
that you can visualize for instance with gnuplot : p ’debug_swap.dat’
u 1:2 w l ; rep ” u 1:3 w l ; rep ” u 1:4 w l ;

C

The goal is to find the most stable geometry for a cluster of two water molecules and one benzene, starting from a geometry where the two water molecules are on different sides of the benzene.

DFTB MEMOSCC DISP EPSMUL
PARAM PTYPE=MAT
/usr/local/deMonNano/basis
QUATERNION NMOL=3 RIGID
1 1.0 0.0 .0 1.0 0.0 0.0 0.0
2 1.0 0.0 3.0 1.0 0.0 0.0 0.0
3 1.0 0.0 6.0 1.0 0.0 0.0 0.0
MOLECULES NMOL=3
1 WAT
2 BZZ
3 WAT

The DFTB line contains slight modifications of the DFTB energy (dispersion correction, weighted Mulliken charges, not detailed here) Find the appropriate Parallel Tempering conditions to get the correct optimized geometry (two water molecules on the same side).

When done, perform the same calculation removing inter-trajectory exhanges (put SMOD=1000000). Conclusion ?

The solutions of the tutorial (input and output files) can be downloaded here : solutions