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[xd0533@163.com]

dear users;
I have done YTaO4  acell geometry  optimization for a long time.But,the 
result is in worse agreement with experimental result.I use TM 
pseudopotentials(LDA).First,I use optcell=0,ionmov=2 to modify nuclear 
positions. I get xred in outfile.Next,I use optcell=2,ionmov=2 to optimize 
acell,and I use xred of just getting as inputfile.The inputfile is as 
follows:  
optcell 2
ionmov  2
ntime  100
ecutsm  0.5
tolmxf 5.0d-4
dilatmx  1.2
#Definition of the k-point grids
kptopt 1                            
nshiftk 1
shiftk  0.5 0.5 0.5  # These shifts will be the same for all grids        
ngkpt  4 4 4
#Definition of the unit cell
acell 9.6584 10.01177 10.3009         
angdeg 90 96.45 90
#Definition of the atom types
ntypat 3         
znucl 39 73 8                           
#Definition of the atoms
natom 12          
typat 3 3 3 3 3 3 3 3 1 1 2 2        
 xred 
 4.8058571790E-01  4.5320614056E-01  2.7776829847E-01
 4.1012786695E-02  2.1174718305E-02  2.8105369766E-01
 1.9414282096E-02  4.5320614056E-01 -2.7776829847E-01
 4.5898721331E-01  2.1174718305E-02 -2.8105369766E-01
 -4.8058571790E-01 -4.5320614056E-01 -2.7776829847E-01
-4.1012786695E-02 -2.1174718305E-02 -2.8105369766E-01
9.8058571790E-01 -4.5320614056E-01  2.7776829847E-01
5.4101278669E-01 -2.1174718305E-02  2.8105369766E-01
2.5000000000E-01  7.5235062898E-01  0.0000000000E+00
-2.5000000000E-01 -7.5235062898E-01  0.0000000000E+00
2.5000000000E-01  2.6379213798E-01  5.0000000000E-01
-2.5000000000E-01 -2.6379213798E-01 -5.0000000000E-01                         
                     
#Definition of the planewave basis set
ecut  35         # I have done ecut convergence 
iscf  7
#Definition of the SCF procedure
nstep 100         
toldfe 1.0d-5                                         
diemac 4.0
Part of the outfile is as follows:
 Unit cell characteristics :
  acell=  1.0692565368E+01  1.1095588474E+01  1.0450404672E+01
  rprim=  9.9999998815E-01  3.2833604208E-31 -1.5393834796E-04
          6.1165109454E-17  1.0000000000E+00 -9.4156560137E-21
         -1.2275216148E-01  7.4401911073E-17  9.9243735664E-01
  ucvol=  1.2304392936E+03 Bohr^3
  lengths=  1.0692565368E+01  1.1095588474E+01  1.0450404672E+01 Bohr
  angles (23,13,12)=  90.00000000  97.05978442  90.00000000 degrees
 Cartesian coordinates (bohr)
  4.96161331301609E+00  4.89728383032503E+00  2.88622266538181E+00
  8.69344139096630E-01  9.81409686207247E-01  2.66179615315217E+00
  3.84669307684909E-01  4.89728383032503E+00 -2.88704566330592E+00
  4.47693848160436E+00  9.81409686207247E-01 -2.66261915107627E+00
 -4.96161331301609E+00 -4.89728383032503E+00 -2.88622266538181E+00
 -8.69344139096631E-01 -9.81409686207247E-01 -2.66179615315217E+00
  1.03078959337171E+01 -4.89728383032503E+00  2.88539966745771E+00
  6.21562675979762E+00 -9.81409686207247E-01  2.66097315522806E+00
  2.67314131035050E+00  8.49957215291789E+00 -4.11498962053044E-04
 -2.67314131035050E+00 -8.49957215291789E+00  4.11498962053044E-04
  2.03173642946528E+00  3.48704012503686E+00  5.18527449508898E+00
 -2.03173642946528E+00 -3.48704012503686E+00 -5.18527449508898E+00
 Cartesian forces (hart/bohr); max,rms= 1.94597E-04 1.02190E-04 (free atoms)
  1.50867868418697E-04 -7.85867827454533E-05 -1.94597458622266E-04
 -3.79472729527827E-05 -5.94519272983165E-05 -9.00750494845077E-05
 -1.50867868418697E-04 -7.85867827454533E-05  1.94597458622266E-04
  3.79472729527827E-05 -5.94519272983165E-05  9.00750494845077E-05
 -1.50867868418697E-04  7.85867827454533E-05  1.94597458622266E-04
  3.79472729527827E-05  5.94519272983165E-05  9.00750494845077E-05
  1.50867868418697E-04  7.85867827454533E-05 -1.94597458622266E-04
 -3.79472729527827E-05  5.94519272983165E-05 -9.00750494845077E-05
 -1.44474277913111E-21  1.61519413253319E-04 -1.07652663224442E-20
 -1.44101465119555E-21 -1.61519413253319E-04  1.34530518594998E-20
 -1.44340705672755E-21  4.57803063226851E-05 -2.08827059393681E-21
 -1.44235037359911E-21 -4.57803063226851E-05  4.77605613099245E-21
 At the end of Broyden step 32, total energy= -1.50239164326113E+02 Ha.
 At Broyd/MD step  32, gradients are converged :
max grad (force/stress)=1.9460E-04<tolmxf=5.0000E-04 ha/bohr (free atoms)     
 
The question is the acell I get is larger than experimental result.Many 
articles refer that the result of LDA is smaller(5%) than experimental 
result.And the error is so largre.I change xc,but there is no effect.Also I 
did ecut convergence.I doubt that the pseudopotentials are not 
suitable.Whether I need to generate pseudopotentials myself? I am puzzled for 
a long time.Can you help me?Thank you in advance.
Best wishes!
xiang