[Pw_forum] Total energy does not coverge with ecut

Timothy Mason thmason24 at yahoo.com
Thu Nov 6 16:44:45 CET 2008


    Gentlemen,

My structures do not see to be converging
with increased ecutwfc.   I'm setting ecutrho to ecutwfc * 12 and using
US PP.    below is a table of ecut values vs energies vs difference
from previous steps followed by my input file followed by part of the output
file.    It appears to begin to converge and 120 ecut but then jumps at
130 and then more at 140.    I understood that convergence should be
pretty well achieved by 30 ecut for US PP.  The only thing I change
between runs are the two ecut parameters.  Any ideas as to what I'm
doing wrong or what I should be expecting?  

A follow up
question in that I'm trying to do vc-relax based on this scf and the
forces decrease until a value of about 0.0003 and then oscillate around
this value.    could that be related to the ecut convergence problem
I'm having?

thanks,

Tim Mason,   University of Missouri St. Louis Department of Physics and astronomy
------------------------------------------------------------------------------------
ecutwfc  total energy    difference from previous 

100    -48.21607621
105    -48.21651331      0.0004371
110    -48.21672787      0.00021456
120    -48.21686396      0.00013609
130    -48.2172448        0.00038084
140    -48.21819748      0.00095268


----------------------------------------------------------------------
&CONTROL
calculation = "scf",
prefix = 'n4_scf.out',
tprnfor = .TRUE.
pseudo_dir = '/home/thmmqc/pwscf/psps/US_GGA',
outdir='/home/thmmqc/tmp'
etot_conv_thr = 1.d-8
/

&SYSTEM
ibrav =
 0, nat = 8, ntyp = 3,
ecutwfc = 100
ecutrho = 1200
celldm(1) = 1.889725989

/

&ELECTRONS
diagonalization = 'cg',
mixing_mode = 'plain',
mixing_beta = 0.7,
conv_thr = 1.0D-8
/


ATOMIC_SPECIES
Li 6.941000 Li.pbe-n-van.UPF
N 14.006740 N.pbe-van_ak.UPF
H 1.007940 H.pbe-van_ak.UPF

CELL_PARAMETERS
10.52658029 -1.08441956 -0.28831668 
-2.96581684 6.61198966 -0.14661465 
1.15738394 0.29429438 3.51384172 

ATOMIC_POSITIONS {crystal}
Li 0.403906747000 0.720101910000 0.473406799000 
Li 0.228004145000 0.310445951000 0.053578743000 
 N 0.230067712000 0.303154666000 0.552891390000 
 N 0.403264134000 0.730145360000 -0.024840278000 
 H 0.185705821000 0.137557379000 0.553855070000 
 H 0.132830606000 0.318409519000 0.624406047000 
 H 0.486061391000 0.685122024000 -0.095482152000 
 H 0.467101514000 0.897467040000 -0.051109646000
 

K_POINTS automatic
2 2 2 0 0 0 

---------------------------------------------------------------------------------------------------------------------

     Program PWSCF     v.4.0.2  starts ...
     Today is  6Nov2008 at  8:30: 1 

     Parallel version (MPI)

     Number of processors in use:       1

     For Norm-Conserving or Ultrasoft (Vanderbilt) Pseudopotentials or PAW

     Current dimensions of program pwscf are:
     Max number of different atomic species (ntypx) = 10
     Max number of k-points (npk) =  40000
     Max angular momentum in pseudopotentials (lmaxx) =  3

     Iterative solution of the
 eigenvalue problem
     Too few procs for parallel algorithm
       we need at least 4 procs per pool

     a serial algorithm will be used


     Planes per process (thick) : nr3 = 96 npp =  96 ncplane =51840
     Planes per process (smooth): nr3s= 54 npps=  54 ncplanes=17280
 
     Proc/  planes cols     G    planes cols    G      columns  G
     Pool       (dense grid)       (smooth grid)      (wavefct grid)
       1     96  32843  1954809   54  10579   357021   2893   
 51177
 


     bravais-lattice index     =            0
     lattice parameter (a_0)   =       1.8897  a.u.
     unit-cell volume          =    1595.0644 (a.u.)^3
     number of atoms/cell      =            8
     number of atomic types    =            3
     number of electrons       =        16.00
     number of Kohn-Sham
 states=            8
     kinetic-energy cutoff     =     140.0000  Ry
     charge density cutoff     =    1740.0000  Ry
     convergence threshold     =      1.0E-08
     mixing beta               =       0.7000
     number of iterations used =            8  plain     mixing
     Exchange-correlation      =  SLA  PW   PBE  PBE (1434)

     celldm(1)=   1.889726 
 celldm(2)=   0.000000  celldm(3)=   0.000000
     celldm(4)=   0.000000  celldm(5)=   0.000000  celldm(6)=   0.000000

     crystal axes: (cart. coord. in units of a_0)
               a(1) = ( 10.526580 -1.084420 -0.288317 )  
               a(2) = ( -2.965817  6.611990 -0.146615 )  
               a(3) = (  1.157384  0.294294  3.513842 )  

     reciprocal axes: (cart. coord. in units 2 pi/a_0)
               b(1) = (  0.098478  0.043373 -0.036069 ) 
 
               b(2) = (  0.015762  0.157902 -0.018417 )  
               b(3) = (  0.008738  0.010147  0.280861 )  


     PseudoPot. # 1 for Li read from file Li.pbe-n-van.UPF
     Pseudo is Ultrasoft + core correction, Zval =  1.0
     Generated by new atomic code, or converted to UPF format
     Using radial grid of  751 points,  2 beta functions with: 
                l(1) =   1
                l(2) =   1
     Q(r) pseudized with  8 coefficients,  rinner
 =    1.000   1.000   1.000


     PseudoPot. # 2 for N  read from file N.pbe-van_ak.UPF
     Pseudo is Ultrasoft, Zval =  5.0
     Generated by new atomic code, or converted to UPF format
     Using radial grid of  729 points,  4 beta functions with: 
                l(1) =   0
                l(2) =   0
                l(3) =   1
                l(4) =   1
     Q(r) pseudized with  8 coefficients,  rinner =   
 0.800   0.800   0.800


     PseudoPot. # 3 for H  read from file H.pbe-van_ak.UPF
     Pseudo is Ultrasoft, Zval =  1.0
     Generated by new atomic code, or converted to UPF format
     Using radial grid of  615 points,  1 beta functions with: 
                l(1) =   0
     Q(r) pseudized with  8 coefficients,  rinner =    0.800

     atomic species   valence    mass     pseudopotential
        Li             1.00     6.94100     Li(
 1.00)
        N              5.00    14.00674     N ( 1.00)
        H              1.00     1.00794     H ( 1.00)

     No symmetry!

   Cartesian axes

     site n.     atom                  positions (a_0 units)
         1           Li  tau(  1) = (   2.6639799   4.4626230   1.4414460  )
        
 2           Li  tau(  2) = (   1.5413893   1.8211812   0.0770139  )
         3           N   tau(  3) = (   2.1626326   1.9176784   1.8319936  )
         4           N   tau(  4) = (   2.0507651   4.3830957  -0.3106026  )
         5           H   tau(  5) = (   2.1879002   0.8711414   1.8724490  )
         6           H   tau(  6) =
 (   1.1765853   2.1450355   2.1090832  )
         7           H   tau(  7) = (   2.9741083   3.9748254  -0.5760977  )
         8           H   tau(  8) = (   2.1961052   5.4124675  -0.4458462  )

     
     Self-consistent Calculation

     iteration #  1     ecut=   140.00 Ry     beta=0.70
     CG style diagonalization
     ethr =  1.00E-02,  avg #
 of iterations =  3.3

     negative rho (up, down):  0.143E-04 0.000E+00

    
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