How to calculate the ground state and excited states energies?. For details please check the attached picture..
You need to optimize the excited state structures first.
For ground state use: opt
For singlet excited states: opt td
For triplet excited states: opt td=triplets
In the ground state of phenol, there are two electrons with opposite spin in HOMO. Therefore, the ground state is a singlet state. After photoexcitation, one electron will go to the excited state, preferably S1. It may go to the higher excited states such as S2 or S3 etc. But it will come down to S1 through internal conversion. From S1, it may go to a triplet state through inter system crossing. This picture shows a schematic of spin configuration in singlet ground state, singlet excited state and triplet excited state (https://upload.wikimedia.org/wikipedia/en/thumb/4/49/ISC_excited_states.png/300px-ISC_excited_states.png). And this is a Jablonski diagram showing the transitions (http://micro.magnet.fsu.edu/primer/java/jablonski/jabintro/jablonskijavafigure1.jpg).
You need to optimize the excited state structures first.
For ground state use: opt
For singlet excited states: opt td
For triplet excited states: opt td=triplets
In the ground state of phenol, there are two electrons with opposite spin in HOMO. Therefore, the ground state is a singlet state. After photoexcitation, one electron will go to the excited state, preferably S1. It may go to the higher excited states such as S2 or S3 etc. But it will come down to S1 through internal conversion. From S1, it may go to a triplet state through inter system crossing. This picture shows a schematic of spin configuration in singlet ground state, singlet excited state and triplet excited state (https://upload.wikimedia.org/wikipedia/en/thumb/4/49/ISC_excited_states.png/300px-ISC_excited_states.png). And this is a Jablonski diagram showing the transitions (http://micro.magnet.fsu.edu/primer/java/jablonski/jabintro/jablonskijavafigure1.jpg).
Dear Uttam Pal ,
Thank you for your comment. I have some more concerns;
Is ground state method is used for ground state energy? Then in Ground State method what is the difference between singlet state and triplet state???? as both options are available in the front box of Spin:
In TD-SCF method: What is the difference between Spin and States? Both show singlet and triplet in their option boxes???
In the ground state if there is an unpaired electron such as in radicals, spin state is called a doublet. If there are two unpaired electrons (as in diradicals), spin configuration may be singlet or triplet (https://upload.wikimedia.org/wikipedia/commons/thumb/7/7e/Spin_multiplicity_diagram.svg/453px-Spin_multiplicity_diagram.svg.png). You should look into "spin multiplicity".
In TD-SCF states mean S1, S2, S3... or T1, T2, T3... etc. as shown in that Jablonski diagram. You need to define the ground state spin configuration as well as the the kind of excited states you want to study (singlets or triplets).
Thanks Uttam Pal a lot for your helpful reply.
Please see the following if I understand correctly:
So if I want to calculate the ground state energy of phenol, I need to use the Method as Ground state and spin as singlet and for O2 the Method as Ground state and spin as triplet.
And for singlet excited state energy of phenol I need to use the method as TD-SCF (instead of ground state), spin as singlet and state as singlet only and for triplet excited energy, the spin will be the same as singlet and state will be changed to triplet only.
Thanks for your cooperation.
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