HOMO-LUMO Calculation and Analysis Using DFT method in Gaussian Software || Part 3 || Gaurav Jhaa

In chemistry, HOMO and LUMO are types of molecular orbitals. The acronyms stand for highest occupied molecular orbital and lowest unoccupied molecular orbital, respectively. HOMO and LUMO are sometimes collectively called the frontier orbitals, such as in the frontier molecular orbital theory.
The energy difference between the HOMO and LUMO is the HOMO-LUMO gap. Its size can be used to predict the strength and stability of transition metal complexes, and the colors they produce in solution. As a rule of thumb, the larger a compound's HOMO-LUMO gap, the more stable the compound.
The HOMO level is to organic semiconductors roughly what the maximum valence band is to inorganic semiconductors and quantum dots. The same analogy can be made between the LUMO level and the conduction band minimum.
In organometallic chemistry, the size of the LUMO lobe can help predict where addition to pi ligands will occur.
A SOMO is a singly occupied molecular orbital such as a half-filled HOMO of a radical. This abbreviation may also be extended to semi-occupied molecular orbital.
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[@girjabaghel7899]

Nice sir

[@muralidharpandey6074]

Very nice video Sir
Sir I have done DFT optimization and job run sufficiently but it's chk file not open

[@RiyaUpadhyay]

is surface and contour only required when we have multiple homo or in each case we have to find homo lumo in the same way?

[@quantumguruji]

When you have degenerate HOMO or LUMO...HOMO-LUMO gap will be same, only MO's will be different. For example, in benzene HOMO and LUMO are doubly degenerate, MO's will be different as the position of node changes (gap will be same).

[@quantumguruji]

In those cases you need to show all of the degenerate MO's

[@girjabaghel7899]

I subscribe to your TH-cam channel sir

[@girjabaghel7899]

Sir ji I am simple chemistry teacher

[@girjabaghel7899]

Sir ji please send your mobile number request

[@paulbk2322]

Sir: please make a video on DFT calculations using broken symmetry approach in Gaussian

[@quantumguruji]

To perform DFT calculations using the broken symmetry approach in Gaussian software, you need to specify certain options in the input file. The broken symmetry approach is commonly used to study systems with open-shell electronic configurations or systems that exhibit spin contamination.

[@khadijaarif2107]

Hi.. When energy gap is calculated to be very small, this value is multilplied or added by a factor to enhance the value of Eg... I can't recoll what was that, can you please tell me?

[@jyotisharma1690]

Why did you not use cube file ?

[@quantumguruji]

You can use it, no issue in that. It's your choice.

[@ajyui847]

Please , I have a question , I have a molecule , I did calculate the HUMO and LUMO energy , now I need to make the calculs for the ion forms of the molecule, how to do it ?

[@quantumguruji]

You need to put the charge value instead of zero. Generally, for neutral molecules, we use 0 charges, but in the case of ions, we use 1,2... to put a + charge and -1, -2...to put negative charges. For more details, follow this video of mine,
th-cam.com/video/LQd9KMfgnPU/w-d-xo.html&ab_channel=QuantumGuruJi

[@ajyui847]

@@quantumguruji thank you , so every time I have an other anion I should make a new calculation !

[@quantumguruji]

@@ajyui847 yes

[@khadijaarif2107]

Hi.. When energy gap is calculated to be very small, this value is multilplied or added by a factor to enhance the value of Eg... I can't recoll what was that, can you please tell me?

[@khadijaarif2107]

Hi.. When energy gap is calculated to be very small, this value is multilplied or added by a factor to enhance the value of Eg... I can't recall what was that, can some body answer me please

[@quantumguruji]

Change it into eV.

[@saidamzil4732]

thank you fro your beautiful video ... Hope you make a tutor video about Ab initio molecular
dynamics (AIMD) simulation 😍😇

[@quantumguruji]

Thank you. More videos to come... stay tuned.... ☺️

[@khadijaarif2107]

Hi.. When energy gap is calculated to be very small, this value is multilplied or added by a factor to enhance the value of Eg... I can't recoll what was that, can you please tell me?

[@khadijaarif2107]

​@@quantumgurujiHi.. When energy gap is calculated to be very small, this value is multilplied or added by a factor to enhance the value of Eg... I can't recoll what was that, can you please tell me?

[@sanjeev1227]

Does gaussian soft ware is available in free if so pls provide link sir if possible it will be helpful to all

[@quantumguruji]

It's commercial software....you need to purchase it

[@sanjeev1227]

@@quantumguruji humo and lumo can be calculated using only by avogadro not taking help of gaussian or gauss view or orca sir

[@quantumguruji]

@@sanjeev1227 dear, avogadro is a visualizer not a software to perform DFT calculations. You can use Orca for DFT and other types of calculations and visualization of the output file could be done in avogadro. Orca is freeware. So you can use it instead of Gaussian.

[@mohammedjishan2027]

Thank You dear, appreciated, put more videos

[@khadijaarif2107]

Hi.. When energy gap is calculated to be very small, this value is multilplied or added by a factor to enhance the value of Eg... I can't recoll what was that, can you please tell me?

[@mohammedjishan2027]

@@khadijaarif2107 usually gaussian gives in Hartree, but you should convert it in to ev. multiply 27.211407953

[@user-jc8rl4kt7c]

There is no Guassian checkpoint file type on my computer. can you help, please!!

[@quantumguruji]

I guess, you didn't gave proper path for checkpoint file so it may be in the scratch folder. Open drive where you have installed gaussian, check for scratch folder...you will find your .chk file there. As it goes there by default.

[@user-jc8rl4kt7c]

@mgurujithank you, can you refer me to some video about it?

[@yassineelhafi6643]

THANK YOU BROTHER

[@khadijaarif2107]

Hi.. When energy gap is calculated to be very small, this value is multilplied or added by a factor to enhance the value of Eg... I can't recoll what was that, can you please tell me?

[@cesnopereiralorenzodossant6180]

sir, is energy on lumo always positive and homo negative? i use a nwchem about COSMO solvation model and get homo and lumo value is negative

[@quantumguruji]

Not always

[@khadijaarif2107]

Hi.. When energy gap is calculated to be very small, this value is multilplied or added by a factor to enhance the value of Eg... I can't recoll what was that, can you please tell me?

[@quantumguruji]

@@khadijaarif2107 please do a wave function stability test, even after its small check for correlation.

[@khadijaarif2107]

@@quantumguruji I found it... It was to convert from hartree to eV... thank you so much 👍

[@quantumguruji]

@@khadijaarif2107 this is also a reason

[@sanvedanashukla2656]

How to install gussion in laptop

[@quantumguruji]

Instructions will be there with software package.

[@user-pi7vp1rn1c]

LUMO is also triply degenerate states so no of LUMO is 3

[@quantumguruji]

yes

[@khadijaarif2107]

Hi.. When energy gap is calculated to be very small, this value is multilplied or added by a factor to enhance the value of Eg... I can't recoll what was that, can you please tell me?

[@quantumguruji]

@@khadijaarif2107there is no such normalisation factor. Better check for correlation effect (static and dynamic), and move accordingly.