The ABINIT Users Mailing List ( CLOSED )

[m.g.p.krishna@chem.leidenuniv.nl]

Dear abinit list,

I am a newbie in 'abinit' program;
and doing a benchmark-calculation on the vibrational frequencies with  
a selected number of planewave codes, including abinit.

As a test case, I used CH4 in an non-orthorhombic box [please see  
below for the setting and files].

I am happy with vibrational calculation with US-PP method,
But When I used PAW potential, I got an error:

  
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


 mkdenpos : WARNING -
  Density went < 0 at    191572 points
  and was set to  1.00E-14.  Lowest was  -0.13E-05.
  Likely due to too low boxcut or too low ecut for pseudopotential  
core charge.

 pawxcm : ERROR -
  Computation of Kxc not yet implemented (choose pawxcdev=0) !

 leave_new : decision taken to exit ...

  
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


After this message, I played accordingly, but still it dont calculates  
due to furthur errors,For ex. when I change: pawxcdev=0, I got a NEW  
error:

 chkint: ERROR -
  Context : the value of the variable ixc is  11.
  The value of the input variable pawxcdev is    0, while it must be
  equal to one of the following:   1   2
  Action : you should change the input variables pawxcdev or ixc.

 leave_new : decision taken to exit ...

  
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

and it goes like this ...

My question:

[1] Does anyone succeeded to calculate the phonon frequencies with PAW  
formalism? Please not: I downloaded different PAW pseudopotential  
files and test this problem. But it doesnt succeed to solve this  
problem. It always stucked with this error.

[2] Trivial question: When I use US-PP I got some -ve frequencies:

 Phonon frequencies in cm-1    :
- -6.922345E+02 -2.256950E+02 -2.072670E+02 -1.258239E+02 -1.010568E+02
- -6.009838E+01  1.208709E+03  1.260028E+03  1.260875E+03  1.491957E+03
-  1.496152E+03  2.929460E+03  3.058923E+03  3.080342E+03  3.081301E+03

How can I reduce the -ve frequencies and get good quality
of frequencies [in methane, we should get degenerate frequencies]

Thanks in advance,

Krishna Mohan G P
Theor.,
University of Leiden
The Netherlands.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Input for SCF calculation:

# Definition of the unit cell unit: Bohr
acell 1 1 1
rprim 8.2385031  -4.756502  0.000000
      8.2385031   4.756502  0.000000
      0.0000000   0.000000 30.32603

# Definition of the atom types
ntypat 2
znucl 1 6

# functional GGA PBE
ixc 11

# Definition of the atoms
natom 5
typat 1 1 1 1 2

# XYZ geometry of the system unit: Amstrong
xangst
     0.62931179   0.62931179   0.62931179
    -0.62931179  -0.62931179   0.62931179
     0.62931179  -0.62931179  -0.62931179
    -0.62931179   0.62931179  -0.62931179
     0.00000000   0.00000000   0.00000000


# Definition of the planewave basis set and PAW
ecut 33
pawecutdg 50

#Definition of the k-point grid

ngkpt  4 4 1
nshiftk 2
shiftk  0.5 0.0 0.0
        0.0 0.5 0.0


# no optimization
ionmov 0
optcell 0

# Definition of the SCF procedure

iscf 7
npulayit 7
nstep 55
toldfe 1.0e-6
diemac 2

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Input used for Vibrational calculation:

#abinit inputdeck

#Response-function calculation, with q=0
  rfphon   1            # Will consider phonon-type perturbation
 rfatpol   1 5          # Only the first atom is displaced 2=natom
   rfdir   1 1 1        # Along the first reduced coordinate axis  1  
1 1 = full pert.
    nqpt   1            # One wavevector is to be considered
     qpt   0 0 0        # This wavevector is q=0 (Gamma)
  kptopt   2            # Automatic generation of k points, taking
                        # into account the time-reversal symmetry only
  tolvrs   1.0d-5       # SCF stopping criterion
    iscf   -3            # Self-consistent calculation, using algorithm 5
  irdwfk   1            # Read the ground-state wavefunctions


# Definition of the unit cell
acell 1 1 1
rprim 8.2385031  -4.756502  0.000000
      8.2385031   4.756502  0.000000
      0.0000000   0.000000 30.32603
# Definition of the atom types
ntypat 2
znucl 1 6

ixc 11
# Definition of the atoms
natom 5
typat 1 1 1 1 2

# using reduced coordinate; get from an easy conversion!
xred
             -5.2835722717E-02  1.9718560289E-01  3.9214725280E-02
              5.2835722717E-02 -1.9718560289E-01  3.9214725280E-02
              1.9718560289E-01 -5.2835722717E-02 -3.9214725280E-02
             -1.9718560289E-01  5.2835722717E-02 -3.9214725280E-02
              0.0000000000E+00  0.0000000000E+00  0.0000000000E+00



# Definition of the planewave basis set and PAW
ecut 33
pawecutdg 50
pawxcdev=0

#Definition of the k-point grid

ngkpt  4 4 1
nshiftk 2
shiftk  0.5 0.0 0.0
        0.0 0.5 0.0

ionmov 0
optcell 0

#Definition of the SCF procedure
nstep  5               # Maximal number of SCF cycles
diemac 9.0             # 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.
                       # The dielectric constant of AlAs is smaller  
that the one of Si (=12).