[QE-users] How H2O molecule reflect DFT scf calculation at 0 Kelvin calculation

[Stefano de Gironcoli]

Dear JAYRAJ ANADANI,

  calculation="scf"  corresponds to a minimization of the total energy 
at fixed atomic positions. you chose where to put the ions. the code 
does its best to return the corresponding energy.

  calculaiton="relax" corresponds to a series of scf calculations, 
followed by forces evaluation and geometry update to minimize the energy 
of the system. The code does its best to converge to a minimum (non 
necessarily the global minimum) in the GS potential energy surface.

  there is no temperature in any of these calculations.

  if you want to simulate the system at finite (classical) temperature 
for the atoms you should perform MD simlations

stefano

On 26/08/22 05:02, Jayraj Anadani wrote:
> Dear QE
>               I put H2O molecular atoms small far apart from each 
> other within large supercell so that the periodic image of the H2O do 
> not interact with each other and run a scf calculation my convergence 
> done successfully with good amount of accuracy upto 10^-9. But it is 
> not reflecting original H2O molecule at 300 Kelvin...but when i 
> relaxing these atoms and then did scf calculation they are reflecting 
> H2O at 300k by observing bond angel and length.. how ? And my question is
> 1) scf is also doing calculation using iteration method algorithm by 
> using electronic densities at ground state so why they converge when 
> two hydrogen atoms and one oxygen atom are not at appropriate 
> distance.still scf converge how ?
> 2) also by doing relax calculation all of sudden two hydrogen and one 
> oxygen come closer and they formed a bond and bond angel which is 
> reflect 300k H2O molecule structure. So how two hydrogen and one 
> oxygen atoms knows during relaxation that i have to make structure at 
> a room temperature?
>
>
> Thank you
> Regards
>
> JAYRAJ ANADANI
> Ph.D Research scholar
> Department of physics
> Sardar Patel University
> Anand,Gujarat,
> India
>
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