Solution LAB2 guanine 2

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Step 1

To calculate HOMO and LUMO level perform an scf and next an nscf calculation adding empty states (e.g. nbnd = 36) Then you can inspect the eigenvalues or:

> grep "highest occupied, lowest unoccupied level"

Step 2

Repeat the same calculation of step 1 by changing the volume of your supercell (e.g celldm(1)=20,25,30). You can also use a script to automatise the runs.

Then collect the results of the energy level as a function of the volume.

Step 4

We can isolate the system in the supercell using an algorithm to correctly treat long-range interactions. In the &SYSTEM name-list insert:

assume_isolated='mt'

This is the Martyna-Tuckerman method: A reciprocal space based method for treating long range interactions in ab initio and force-field-based calculations in clusters G. Martyna, M. Tuckerman J. Chem. Phys. 110 2810 (1999)