VASP calculation while maintaining the ratio of the lattice constants

[arkulkarni245]

Hello,
I am a relatively new VASP user, so please excuse if my question is too obvious!
I am trying to find the minimum geometry configuration of a periodic system that is isotropic in reality i.e. a = b = c and alpha = beta = gamma = 60. Because of the large system size of the 'real' isotropic system (~ 1000 atoms), I would like to use a smaller 'anisotropic' system but maintain that a, b and c remain equal and the angles are fixed at 60 deg. The current approach that I am using, is to relax the internal coordinates (ISIF = 2) for different values of a=b=c and find the lattice constants that give the minimum energy.
Is there another way of doing this? Can I find the optimum lattice constants directly while maintaining the ratio of the unit cells? Is there a way to specify the symmetry in the POSCAR file?
Thank you.

[admin]

no, unfortunately not, the only way to do this lattice constant optimization is the way you do it