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[dylu@ucdavis.edu]

Dear Abinit users:
     I'm trying to reproduce the static dielectric matrices of bulk silicon 
as in Ref. 1 with Abinit. The input file is listed at the bottom. After 
several tests, my basic concern is about the accuracy. Following a similar 
recipe in Ref. 1, I found that my computed macroscopic dielectric constant 
(12.5708) and macroscopic dielectric constant without local field (14.0011) 
are about 3% larger than the values reported in the reference (12.2) and 
(13.61). For the diagonal matrix elements of epsilon_tilde^-1 (E^-1) , other 
than near Gama point (q->0), the difference is about 20% for the heading 
elements and even larger for other elements. The results are compared here:

              E^-1_{0,0}(q->0) E^-1_{111,111}(q->0) E^-1_{0,0}(X) 
current work      0.079549        0.596704            0.328162
Ref. 1             0.082           0.595               0.2749
EXP                0.085

           E^-1_{11-1,11-1}(X) E^-1_{0,0}(L) E^-1_{-1-11,-1-11}(L)
current work      0.930791        0.333795            0.975889
Ref. 1             0.4138          0.2828              0.4822

     The only reason I could imagine is the pseudopotential 14si.pspnc I 
used, not the same as the one in Ref. 1 generated by the authors following 
Kerker algorithm.

     Could someone with more experiences give me some comments? Is a better 
pseudopotential the only thing I need?

     Thanks
     Deyu Lu

****************************************************************************

Ref. 1: Ab initio static dielectric matrices from the density-functional 
approach.
I. Formulation and application to semiconductors and insulators, M. Hybertsen 
and S. Louie, PRB, 35:5585, 1987.

*****************************Input file *************************************
ndtset     2

# Definition of parameters for the calculation of the KSS file
nbandkss1   -1         # Number of bands in KSS file (-1 means the maximum 
possible)
nband1      9         # Number of (occ and empty) bands to be computed
istwfk1     60*1

# Calculation of the screening (epsilon^-1 matrix)
optdriver2  3        # Screening calculation
getkss2     -1       # Obtain KSS file from previous dataset
nband2      72       # Bands to be used in the screening calculation
ecutwfn2    8.5      # Cut-off energy of the planewave set to represent the 
wavefunctions
ecuteps2    8.5      # Cut-off energy of the planewave set to represent the 
dielectric matrix
ppmfrq2    16.7 eV  # Imaginary frequency where to calculate the screening
nqptdm2     3
qptdm2     0.000010    0.000020    0.000030
          -0.500000   -0.500000    0.000000
           0.500000    0.500000    0.500000

# Data common to the three different datasets

# Definition of the unit cell: fcc
acell  3*10.217        # This is equivalent to   10.217 10.217 10.217
rprim  0.0  0.5  0.5   # FCC primitive vectors (to be scaled by acell)
       0.5  0.0  0.5
       0.5  0.5  0.0

# Definition of the atom types
ntypat  1         # There is only one type of atom
znucl 14          # 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 Silicon.

# Definition of the atoms
natom 2           # There are two atoms
typat  1 1        # They both are of type 1, that is, Silicon.
xred              # Reduced coordinate of atoms
      0.0  0.0  0.0
      0.25 0.25 0.25


# Definition of the k-point grid
kptopt  1            # Option for the automatic generation of k points,
nkpt    60
ngkpt   8 8 8
nshiftk 4
shiftk  0.5 0.5 0.5  # These shifts will be the same for all grids
        0.5 0.0 0.0
        0.0 0.5 0.0
        0.0 0.0 0.5

# Use only symmorphic operations
symmorphi 0

# Definition of the planewave basis set (at convergence 16 Rydberg 8 Hartree)
ecut 8.5          # Maximal kinetic energy cut-off, in Hartree

# Definition of the SCF procedure
nstep   10        # Maximal number of SCF cycles
toldfe  1.0d-6    # Will stop when this tolerance is achieved on total energy
diemac  12.0      # Although this is not mandatory, it is worth to