Dear Mr Rajib K. Sutradhar

Python's pyscf library is commonly used to compute density functional theory (DFT). There is, however, a separate software package called siesta that can be used for DFT calculations, and it has a Python interface known as pysiesta.

With Pysiesta, you can use Python scripts to perform DFT calculations with the electronic structure code Siesta. Within the Python environment, it is possible to generate input files for siesta, run calculations, and analyze results.

In order to use pysiesta, you must have both siesta and pysiesta installed on your computer. A detailed description of how to install and use Pysiesta can be found in the Pysiesta documentation.

Here is an example of code:

import pysiesta as siesta

# set up the calculation

calc = siesta.Calculation(label='water',

mesh_cutoff=200 * siesta.Ry,

xc='PBE',

kpts=[4, 4, 1],

convergence={'energy': 1e-4},

species=['H', 'O'],

basis_set='SZP',

occupations='smearing',

temperature=300 * siesta.K)

# create the structure object

water = siesta.Structure(coordinates=[(0.000000, 0.000000, 0.000000),

(0.757163, 0.586302, 0.000000),

(-0.757163, 0.586302, 0.000000)],

species=['O', 'H', 'H'])

# set up the job

job = siesta.SiestaCalculation(calculation=calc, structure=water, mpi=True)

# run the job

job.run()

# get the total energy

total_energy = job.results.get_total_energy()

print(f'The total energy of the water molecule is {total_energy:.4f} Ry')

In this example, we set up a Calculation object with the desired parameters for the DFT calculation, including the exchange-correlation functional (xc), the k-point mesh (kpts), the basis set (basis_set), and the temperature (temperature) for the smearing method. We then create a Structure object for the water molecule and set up a SiestaCalculation object with the calculation and structure. Finally, we run the calculation with job.run() and retrieve the total energy from the job.results object.

Thanks dear.