The ABINIT Users Mailing List ( CLOSED )

["Zhenhua Zeng" <myid520@163.com>]

Hello,

Please see the FAQ first. The content scfcge: ERROR - Potential-based CG line minimization not converged refer to your problem.It has beed discussed a lot. You can try it.
good luck,

> Dear  users,
> I have some problems with the structural optimization procedure,
> and I would like to know if some of you can give me some hints 
> to solve it.
> I have interest in the calculation of the electronic properties
> of alloys, and I'm using a small supercell to compute AlN+O.
> As previous steps, I need to relax the atomic positions of 
> oxygen and its 4 nearest neighbors Al, keeping the rest
> of the atoms fixed.
> I have choosed the option ionmov = 2, allowing the O to move 
> only in the Z axis, the same that the apical Al, the other
> 3 Al are allowed to move without restrictions.
> However, the program craches in the first BROYDEN step,
> after several oscillation of the values of vres2.
> There are some WARNING messages for the second derivative
> and Potential minimization convergence as :
> 
>  scfcge: WARNING -
>   Potential-based CG line minimization has trouble to converge.
>   The algorithm is restarted with more secure parameters.
>  scfcge: actual   27-13-2   1.7263E-01 -1.033400607802E+02  3.5945E-08
>  scfcge: predict           -2.0000E+00 restart the algorithm
>  scfcge:
>  scfcge: start    27-14-0   0.0000E+00 -1.033400607802E+02  3.5945E-08
> 
> findmin : WARNING -
>   (scfcge) The second derivative is negative, equal to -1.5892399770E-17.
>  findmin : lambda_predict   5.7012E+00 etotal_predict  -1.0334006078E+02
>  scfcge: actual   31-15-1   5.0351E+00 -1.033400607802E+02  4.6820E-09
>  scfcge: predict            5.7012E+00 not close enough => continue minim.
> 
> and finally the program stops with the message:
> 
> scfcge : ERROR -
>   Potential-based CG line minimization not converged after 13 restarts.
>   Action : read the eventual warnings about lack of convergence.
>   Some might be relevant. Otherwise, raise nband.
> 
> I am using the version 4.3.3 of Abinit, compiled on a SGI 
> cluster under linux, 
> in the botton the input file is attached.
> I will appreciate your commentaries,
> 
> Best regards,
> Daniel Olguin
> 
> 
> # Crystalline AlN+O : computation of the total energy
> # relax only: O +/- z, Al_1 +/- z & Al_2 +/- xyz
> 
> # usin low values for ecut, test vars to relax ions
> 
>   kptopt   1           # Automatic generation of k points. Take fully into
>                         # account the symmetry to generate k only in the
>                         # irreducible BZ
>   tolvrs   1.0d-18     # SCF stopping criterion
>   tolmxf   5.0d-4      # tolerance maximal force
>   mtime    40          # time steps in the Broyden structural optimization
>   iscf     5           # Self-consistent calculation, using algorithm 5
> 
> #Definition of the k-point grid
>   ngkpt    5 5 6       # grid based on lapw 200 kpt
> 
>   nshiftk   1           # for hexagonal lattices
>   shiftk    0.0 0.0 0.5
> 
> # Definition of the unit cell (using optimized values, )
> 
>   acell 6.154 6.154 4.923 angstrom # lattice parameter cell 221
> 
>   angdeg  90. 90. 120.                 # Angles in degrees
> 
>  iatfix 2 3 4 5 6 7 8 13 14 15 16  # all N are fixed, the Al nn N fixed
> 
>  iatfixx 1 9         # x-coordinate of O and Al_9 is fixed
>  iatfixy 1 9         # y-coordinate of O and Al_9 is fixed, ie. only Z-mov.
> 
>  ionmov 2            # using option 2 
> 
>  natfix 11           # 11- fixed atoms, from the grand total: 16 
>  natfixx 2           # the allowed O & Al_9 are fixed in X-
>  natfixy 2           # and also, fixed in Y-axis
> 
> # Atoms in the unit cell
>   ntypat    3           # There are 3 types of atoms
>   znucl     8 7 13        # Atom 1 is O, atom 2, N, atom 3 Al
>   natom     16          # There are two atoms in the unit cell
>   typat     1 7*2 8*3  # The first class is O, the second, N, third Al
>   xred                  # Reduced coordinates
>    0.             0.             0.      # atom 1
>    0.333333333333 0.166666666667 0.5000  # Reduced coordinate of atom 2
>    0.833333333333 0.166666666667 0.5000  # Reduced coordinate of atom 3
>    0.833333333333 0.666666666667 0.5000  # Reduced coordinate of atom 4
>    0.             0.5            0.      # atom 5
>    0.5            0.             0.      # atom 6
>    0.5            0.5            0.      # atom 7
>    0.333333333333 0.666666666667 0.5000  # Reduced coordinate of atom 8
>    0.             0.             0.6323  # atom 9
>    0.333333333333 0.166666666667 0.1323  # atom 10
>    0.833333333333 0.166666666667 0.1323  # atom 11
>    0.833333333333 0.666666666667 0.1323  # atom 12
>    0.             0.5            0.6323  # atom 13
>    0.5            0.             0.6323  # atom 14
>    0.5            0.5            0.6323  # atom 15
>    0.333333333333 0.666666666667 0.1323  # atom 16
> 
> # Given the number of band explicitely (no use the default value)
>   nband     40
> # Exchange-correlation functional
> # ixc  1                 # LDA Teter Pade parametrization
> 
> #Definition of the planewave basis set
>   ecut   50.0       # Maximal kinetic energy cut-off, in Hartree
> 
> #Definition of the SCF procedure
>   nstep     100        # Maximal number of SCF cycles
>   diemac    9.14       # this is the static dielectric constant of AlN, exp
> 
> 

Zhenhua Zheng
Hunan University PR. China

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