## Firefly and PC GAMESS-related discussion club

Learn how to ask questions correctly

** Re: HOMO-LUMO GAP CALCULATION DOUBT.... **
Thomas

thomaspijper@hotmail.com

Dear Siddheshwar,I'm not sure if I understand your question correctly. However, I would like to propose that you should calculate the HOMO-LUMO gap with:

Gap = LUMO - HOMO = 2.2 eV

which gives a positive number that looks normal to me.

Kind regards,

Thom

On Sat Apr 20 '13 9:34pm, Siddheshwar Chopra wrote

--------------------------------------------------

>Dear Sir,

>As learnt from the same forum about calculating HOMO-LUMO, I have got the final result as follows:

>Orbital No. (in eV)

>161 LUMO -2.25 A

>160 HOMO -4.45 A

>Hence the GAP= HOMO-LUMO = -2.2 eV

>Now the doubt is that when I plotted the Density of states spectrum, I get to see a gap between the occupied and virtual orbitals (I have attached an image of it for your reference).. Please help me understanding this concept... Just now the calculations have shown a negative value, which in my opinion means overlapping occupied and virtual orbitals. Then how can a gap be seen? Am I going wrong in the calculations or something else. Please help..

>Regards,

Sun Apr 21 '13 3:01pm

This message read **1090** times