[Pw_forum] Re: cut-off radius for radial integrations

Virginie Quequet virginie.quequet at polytechnique.fr
Tue Feb 22 14:46:09 CET 2005


Tank you for your reply.
It seems quite systematic, because my first example was for titanium and
I tried for silicon with the input of example01 (david) with a pseudo-potential 
with non-local part defined up to 60 a.u. and I obtain this

rcut = 10 a.u.

!    total energy              =   -15.89013028 ryd
     estimated scf accuracy    <        6.7E-09 ryd
                                                                                                                               
     band energy sum           =     0.62621995 ryd
     one-electron contribution =     4.74024554 ryd
     hartree contribution      =     1.07806794 ryd
     xc contribution           =    -4.80868510 ryd
     ewald contribution        =   -16.89975867 ryd
                                                                                                                               
     convergence has been achieved
                                                                                                                               
     Forces acting on atoms (Ry/au):
                                                                                                                               
     atom   1 type  1   force =     0.00000000    0.00000000    0.00000000
     atom   2 type  1   force =     0.00000000    0.00000000    0.00000000
                                                                                                                               
     Total force =     0.000000     Total SCF correction =     0.000000
                                                                                                                               
                                                                                                                               
     entering subroutine stress ...
                                                                                                                               
          total   stress  (ryd/bohr**3)                  (kbar)     P=  -17.45
  -0.00011860   0.00000000   0.00000000        -17.45      0.00      0.00
   0.00000000  -0.00011860   0.00000000          0.00    -17.45      0.00
   0.00000000   0.00000000  -0.00011860          0.00      0.00    -17.45
                                                                                                                               
                                                                                                                               
rcut = 60 a.u.

!    total energy              =   -15.90406433 ryd
     estimated scf accuracy    <        5.9E-09 ryd
                                                                                                                               
     band energy sum           =     0.61224706 ryd
     one-electron contribution =     4.72633379 ryd
     hartree contribution      =     1.07803417 ryd
     xc contribution           =    -4.80867362 ryd
     ewald contribution        =   -16.89975867 ryd
                                                                                                                               
     convergence has been achieved
                                                                                                                               
     Forces acting on atoms (Ry/au):
                                                                                                                               
     atom   1 type  1   force =     0.00000000    0.00000000    0.00000000
     atom   2 type  1   force =     0.00000000    0.00000000    0.00000000
                                                                                                                               
     Total force =     0.000000     Total SCF correction =     0.000000
                                                                                                                               
                                                                                                                               
     entering subroutine stress ...
                                                                                                                               
          total   stress  (ryd/bohr**3)                  (kbar)     P=  -25.60
  -0.00017399   0.00000000   0.00000000        -25.60      0.00      0.00
   0.00000000  -0.00017399   0.00000000          0.00    -25.60      0.00
   0.00000000   0.00000000  -0.00017399          0.00      0.00    -25.60
                                                                                                                               
                                                                                                                               
Virginie Quequet


 


On Thursday 17 February 2005 16:22, Virginie Quequet wrote:

> I try to change to 60 a.u. the cut-off radius for radial integration,

you shouldn't: the radial integration is performed on short-range
functions only. Beyond 10 a.u. all you have is numerical noise.

> which is put to 10 a.u. in the code (rcut variable). It seems to me 
> that it should change very little the results, but it is not the case.

please provide a test case (input and output) 

Paolo






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