[CPMD-list] too long Si-O bond-length from geometry optimization

[liu liuxiandong]

Dear CPMDers,

I used CPMD to optimize a mineral containing Si, Al, O and H within a fixed
cell. The bond lenths of Al-O, O-H are very close to the experimental
values, whereas the Si-O lengths are about 1.72 angstrom, much longer than
the experimental value (about 1.61 angstrom). Could you give some
suggestions ?
The following is part of the input file.
&CPMD



  OPTIMIZE GEOMETRY
XYZ
  HESSIAN
UNIT



  CONVERGENCE
ADAPT

  0.02

  CONVERGENCE
INITIAL

  1.0D-4

  CONVERGENCE
ORBITALS
  5.0D-5

  CONVERGENCE
GEOMETRY
  4.0D-4



    ODIIS
NO_RESET=40


5



    LBFGS
NREM


20


&END



&DFT

  FUNCTIONAL
BLYP





&END



&SYSTEM




SYMMETRY


14


ANGSTROM

  CELL ABSOLUTE
DEGREE

   5.1535 8.9419 7.3906 91.9260 105.0460 89.7970


CUTOFF

   70.0

&END



&ATOMS

*O_MT_BLYP.psp
KLEINMAN-BYLANDER

 LMAX=P

 18
...


*H_MT_BLYP.psp
KLEINMAN-BYLANDER

 LMAX=S

 8
...


*Si_MT_BLYP.psp
KLEINMAN-BYLANDER

 LMAX=P

 4
...


*Al_MT_GIA_BLYP.psp
KLEINMAN-YLANDER
 LMAX=D
LOC=0

 4
...


&END
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