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### pressure dependence of band gap

Posted:

**Tue Aug 28, 2018 11:02 am**
by **new_986**

Hi all

I want to calculate band gap of a perovskite structure at different pressures, first I did cell optimization of different pressures, then I used optimized lattice constant and relaxed atomic coordinates as inputs to calculate band gap

As it's known band gap should increase with increasing pressure, but from pressure 1 Gpa to 5 Gpa , my band gaps decreasing, my question is:

Is this a correct way to calculate pressure dependence band gap? if no , what method I should use in abinit? if yes why this is happening with me?

regards

Nawzad

### Re: pressure dependence of band gap [SOLVED]

Posted:

**Wed Sep 12, 2018 11:39 am**
by **ebousquet**

Dear Nawzad,

I would say that the band gap will have the tendency to reduce with pressure in general, no? But I might be wrong, do you have references that show increase of the band gap under pressure in perovskites? Of course this could depend on the system...

Best wishes,

Eric

### Re: pressure dependence of band gap

Posted:

**Fri Sep 14, 2018 11:56 am**
by **new_986**

Dear Eric

Yes band gap reduces with increasing of pressure...but I have seen in references, for example, for CsPbI3 phase transition happens from cubic to orthohombic before 0.4 Gpa, But I have increased pressure up to 1 Gpa,

my question is, How I know when phase changes in abinit?

Thanks for replying and help

Nawzad

### Re: pressure dependence of band gap

Posted:

**Mon Sep 24, 2018 10:15 am**
by **rajaraman**

Dear Nawzad,

calculate total energy as a function of pressure for both cubic and orthorhombic structures.

there will be crossover at some pressure (you said experimental one is 0.4GPa).

You have to use the bandgaps corrosponding to minimum energy structure at each pressure.

regards

-rajaraman

### Re: pressure dependence of band gap

Posted:

**Tue Oct 02, 2018 12:39 pm**
by **new_986**

rajaraman wrote:Dear Nawzad,

calculate total energy as a function of pressure for both cubic and orthorhombic structures.

there will be crossover at some pressure (you said experimental one is 0.4GPa).

You have to use the bandgaps corrosponding to minimum energy structure at each pressure.

regards

-rajaraman

Dear rajaraman

Thanks a lot for the reply,,, I will try that

Regards

Nawzad

### Re: pressure dependence of band gap

Posted:

**Mon Nov 05, 2018 11:05 am**
by **new_986**

rajaraman wrote:Dear Nawzad,

calculate total energy as a function of pressure for both cubic and orthorhombic structures.

there will be crossover at some pressure (you said experimental one is 0.4GPa).

You have to use the bandgaps corrosponding to minimum energy structure at each pressure.

regards

-rajaraman

Dear rajaraman

I have calculated total energy of cubic and tetragonal of CsPbCl3 , but it gives me same energy for both structures

any help plz?

best regards

Nawzad