[CPMD-list] question about CUTOFF

[liu liuxiandong]

Dear CPMD users,

  I want to optimize the geometry of a silicate material. The
following is part of the input,
&CPMD	
 RESTART WAVEFUNCTIONS COORDINATES HESSIAN	
 OPTIMIZE GEOMETRY XYZ
 HESSIAN UNIT

 CONVERGENCE ORBITALS
 5.0D-6
 CONVERGENCE GEOMETRY
 5.0D-4

 PCG MINIMIZE
 TIMESTEP
 10
 LBFGS NREM
 40
 LSD

&END
...
&SYSTEM
  CUTOFF
   70.0
....
&END

&ATOMS

ISOTOPES
...
*O_MT_BLYP.psp KLEINMAN-BYLANDER
 LMAX=P
*H_MT_BLYP.psp KLEINMAN-BYLANDER
 LMAX=S
*Si_MT_BLYP.psp KLEINMAN-BYLANDER
 LMAX=D
*Al_MT_GIA_BLYP.psp KLEINMAN-BYLANDER
 LMAX=D LOC=0
*Fe_MT_BLYP_NLCC.psp NLCC KLEINMAN-BYLANDER
 LMAX=D LOC=S
*Na_SEMI_BLYP.psp KLEINMAN-BYLANDER
 LMAX=P
...............
The total energy of the relaxed structure is  -983.949852 at CUTOFF 70Ry.
Then I increased CUTOFF to 75 Ry and performed single-point
calculation with this optimized structure,  the total energy decreased
to about -984.845447.

Since such LSD calculation is very time demanding, is it necessary to
optimize the structure with higher CUTOFF ?
Thanks.

Xiandong Liu