4.6. Example: HNO3(H2O)10 in Electric Field

Tip

The sample input and output files can be found in testfiles/rigidmol/3-electricfield.

Now you can easily perform a global optimization of the cluster \(\mathrm{HNO}_3\left(\mathrm{H}_2\mathrm{O}\right)_{10}\). Basically, the following two files ef-0.inp and ef-0.cluster are needed:

ef-0.inp

ef-0.cluster # cluster file name
30           # population size
50           # maximal generations
3            # scout limit
10.00000000  # amplitude
ef-0         # save optimized configuration
30           # number of LMs to be saved

ef-0.cluster

2
hno3.xyz    1
tip4p.xyz   10
* 10.0000

After copying misc/charmm/hno3.xyz and misc/charmm/tip4p.xyz to the current path, you can run the global optimization by:

$ rigidmol ef-0.inp > ef-0.out

After a few seconds, You will find the global minimum in ef-0-OPT.xyz and local minima in ef-0-LM.

So, what will \(\mathrm{HNO}_3\left(\mathrm{H}_2\mathrm{O}\right)_{10}\) look like in an electric field, say \(F\) = 0.8 V Å ^-1? We want to store the results in ef-8*, so first we prepare the input file ef-8.inp which is very similar to ef-0.inp:

ef-8.inp

ef-8.cluster # cluster file name
30           # population size
50           # maximal generations
3            # scout limit
10.00000000  # amplitude
ef-8         # save optimized configuration
30           # number of LMs to be saved

Now prepare ef-8.cluster. You should add the electric field strength in the first line:

ef-8.cluster

2  0.8
hno3.xyz    1
tip4p.xyz   10
* 10.0000

Now you can run the global optimization by:

$ rigidmol ef-8.inp > ef-8.out

Below are the global minima of \(\mathrm{HNO}_3\left(\mathrm{H}_2\mathrm{O}\right)_{10}\) in vacuum and in the static electric field (ef-0-LM/0.xyz and ef-8-LM/0.xyz). Obviously, the electric field elongates the cluster.