## Firefly and PC GAMESS-related discussion club

Learn how to ask questions correctly

Re^3: Is there a Simple way to know HOMO-LUMO gap?

Solntsev Pasha
solntsev@univ.kiev.ua

I am not Alexei, but maybe attached picture will be useful.

Pavel.

On Tue Feb 5 '13 7:10am, Siddheshwar Chopra wrote
-------------------------------------------------
>Dear Alexei,
>I am actually running HESSIAN calculations. I looked for the string "EIGENVECTORS", and then nos. 149 and 150. But I still failed to get the HOMO-LUMO... I am atatching herewith a sample fiel for your reference. Please let me know the value of HOMO-LUMO from it..

>Regards,
>
>
>
>On Mon Feb 4 '13 11:38pm, Alexei Popov wrote
>--------------------------------------------
>>Hello,

>>this can be done very simple.

>>Run single point SCF energy calculation. Look at the output and you'll see strings like these:

>> TOTAL NUMBER OF SHELLS              =   10
>> TOTAL NUMBER OF BASIS FUNCTIONS     =   38
>> NUMBER OF ELECTRONS                 =   12
>> CHARGE OF MOLECULE                  =    0
>> STATE MULTIPLICITY                  =    1
>> NUMBER OF OCCUPIED ORBITALS (ALPHA) =    6
>> NUMBER OF OCCUPIED ORBITALS (BETA ) =    6

>>Orbital #6 is HOMO and orbital #7 is LUMO.

>>Look at the section

>> FINAL ENERGY IS....
>>
>>
>>          ------------
>>          EIGENVECTORS
>>          ------------

>>and find the eigen-vectors #6 and #7 (they are numbered so it is easy)
>>The numbers above the eigen-vectors are their energies. Substract two numbers for two orbitals and you'll get the answer.

>>Cheers,
>>Alexei Popov
>>
>>
>>
>>On Mon Feb 4 '13 12:41pm, Siddheshwar Chopra wrote
>>--------------------------------------------------
>>>Dear Sir,
>>>Please forgive me for asking this question perhaps again in this forum. Actually I have completed the HESSIAN run and am able to read the HOMO,LUMO energies USING GABEDIT software. But I find it really too involving and error prone to calculate the HOMO-LUMO gap from the data. Please suggest em a simpler way so that I get the HOMO-LUMO gap directly...IS there any COMMAND I could add in the FIREFLY input file to get HOMO-LUMO printed in the output file directly?
>>>If a command line input is not available, can Prof. Alex add ONE such command for the users?

>>>Regards,

Homo-Lumo

Tue Feb 5 '13 9:02am