# Solution LAB2 guanine 3

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- Back to the previous page: Electronic properties of isolated molecules#Exercise 3

For calculation of E(N-1) we need to set the following flags in the &SYSTEM namelist:

nspin=2 ! Note, now we have unpaired electrons: tot_charge=+1 ! charged system tot_magnetization=1 ! we need to set a total magnetisation

Also, the following option needs to be used for charged systems :

assume_isolated="mt"

Using ecutwfc=50 Ry and 35 au of cell size,

E_tot(N) = -193.48101821 Ry E_tot(N-1) = -192.89782124 Ry

giving

IP = E_tot(N-1) - E_tot(N) = 0.58319697 Ry = 7.934861 eV

now much closer to the experimental value of 8.0-8.3 eV.

Interestingly, one can run the same set of calculations also using different functionals, including GGAs (PBE), meta-GGAs (eg TPSS or SCAN), hybrids (PBE0), or HF itself.

In order to do this, you can force e.g. the functional from input, by using:

&SYSTEM [...] input_dft="PBE0" /

How do -eps_HOMO and delta-scf values compare ?