[Pw_forum] problem in vc-relax/ relax

[Elio Physics]

Dear all,
I am trying to optimize a structure I am working on. Firstly, I try to find what is the lattice constant that gives the minimum energy. When this value is used and an scf calculation is performed, The pressure is not exactly zero ( ~ - 2.45 Kbars) and the forces on individual atoms are still large. So I try to relax the structure using calculation =' relax'., which works pretty fine. However, due to the differences in the scf calculation performed by 'relax' and by 'scf', I again get a pressure of -2.45 and a large force when I run an scf calculation.  I also realized that  P ~ 0 and forces are pretty low at a value of the lattice constant different from the one above (which gives the minimum energy). Can anyone tell me what can be done? how can i get low forces keeping the equilibrium lattice constant intact? Is it possible to use a lattice constant which does give a minimum energy structure but retains both P and Forces almost zero?
Any advice is highly appreciated.
ElioDerby university 
 		 	   		  
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