Mr. Selvaratnam,

By Gaussian (www.gaussian.com) and GaussView (http://gaussian.com/gaussview6/).

Have you tried Vesta? You can use it to generate crystals of any size and shape from a .cif crystal structure file, and output the result in a number of formats, including .xyz

http://jp-minerals.org/vesta/en/

Avogadro can also be useful. It's not designed specifically to work with periodic structures like Vesta, but if you want to edit surface species, it does the job. It can also output .xyz files.

https://avogadro.cc/

Both software are available for free.

I agree with Gabriel Jeantelot .

Thank you for the answers. I've tried Avogadro and ASE. I'll try with VESTA and GV.

Thank you

Bala

'In theory, theory and practice agree. In practice, they do not.'

I would believe one well-conducted experiment versus a paper with more Greek letters than an Athens post office.