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[jiangx3@rpi.edu]

Dear all,

I am doing the optimization of styrene and it comes out that the gradient 
is hard to converge. I am wondering why that happens. If anyone has some
suggestion about this, would you please tell me? Thanks in advance!


Best regards,
Xueping Jiang






# H2 molecule in a big box
#
# This file to optimize the H2 bond length, compute the associated total
# energy, then to compute the total energy of the isolated H atom.
# Here, a double loop has been used.
#


 ecut 30

 nband 40
# Dataset1: usual self-consistent ground-state calculation with
# optimization of ionic positions

prtden  1         # Print the density, for use by dataset 2
ionmov  2         # Conduct structural optimization
optcell 0         # Optimization of the ionic positions only
ecutsm  0.5       # Energy cutoff smearing
ntime   20        # number of structural optimization steps

acell     1.3891769137E+01  1.6040863257E+01  3.7793676801E+01 Bohr
#defination of the unit cell
rprim  1.0     0.0   0.0   # primitive vectors (to be scaled by acell)
       0.0     1.0   0.0
       0.0     0.0   1.0
chkprim 0

ntypat 2          # There is only one type of atom
znucl 6 1          # The keyword "znucl" refers to the atomic number of the 
                  # possible type(s) of atom. The pseudopotential(s) 
                  # mentioned in the "files" file must correspond
                  # to the type(s) of atom. Here, the only type is Hydrogen.
natom 16           # There are two atoms
                         

#Definition of the atoms
typat 8*1 8*2        # For the first dataset, both numbers will be read,
                  # while for the second dataset, only one number will be rea
xangst             1.72520127    3.32947924    0.00000000
                   2.95040254    2.62211481   -0.00000000
                   5.40080508    2.62211481   -0.00000000
                   4.17560381    3.32947924    0.00000000
                   6.62600635    3.32947924    0.00000000
                   1.72520127    4.74422962   -0.00000000
                   2.95040254    5.45159405    0.00000000
                   4.17560381    4.74422962    0.00000000
                   2.95040254    6.42529405    0.00000000
                   0.88195059    5.23107660    0.00000000
                   0.88195059    2.84263226    0.00000000
                   2.95040254    1.64841481    0.00000000
                   5.40080508    1.64841481    0.00000000
                   7.47126426    2.84612560    0.00000000
                   6.62600635    4.26317924    0.00000000
                   4.98421340    5.21107672    0.00000000
#Definition of the k-point grid
kptopt 1          # Enter the k points manually 
ngkpt 12 12 1            # Only one k point is needed for isolated system,
                  # taken by default to be 0.0 0.0 0.0
toldff 5.0d-6        # Will stop the SCF cycle when, twice in a row,
                         # the difference between two consecutive evaluations 
of
                         # forces differ by less than toldff (in Hartree/Bohr)

#Definition of the SCF procedure
nstep 100          # Maximal number of SCF cycles
#toldfe is no more defined, as toldff is used above... 
diemac 4.0        # Although this is not mandatory, it is worth to
                  # precondition the SCF cycle. The model dielectric
                  # function used as the standard preconditioner
                  # is described in the "dielng" input variable section.
                  # Here, we follow the prescriptions for molecules
                  # in a big box