[Pw_forum] fpmd.x questions...

[Matt Small]

  Dear pwscf users,

  I'm relatively new to pwscf, and would like to ask a
few general questions which I haven't really been able
to find the answers to in either the input files,
manual, or on the forum.  This may be because I want
to use fpmd.x for my calculations and most of the
material in these sources involves pw.x.
   
     1) In the input file it says to use ibrav=14 for
variable cell cp type 
         calculations. Is this a typo? (both cp and pw
use ibrav=0 for vc 
         calculations)
     
     2) How do you choose the size of your supercell?
I got the
         impression that this is what the cell
parameters are for, but
         have not found any confirming information.

     3) The runs that I've been doing aren't
stabilizing at the temp.s 
         or the pressures that I want. In part, I
realize this will be due to
         the simulation length and cell size; but for
some reason my
         system does not start at the given starting
temperature. I'm not
         starting with an scf relaxtion (want to make
sure I know how to
         do the md calculations first) but that really
shouldn't matter.

     4) How do I get the Entropy, Enthalpy, and Heat
Capacity? And
         are k-points or gamma points better for over
all bulk properties?
                 - In fpmd.x I realize the Enthalpy is
given, but there also
                    appears to be a fortran file
"enthropy" (??) which I
                    presume refers to entropy - how do
I activate it?
                 - I know it's possible to get the
heat capacity via the relat-
                    ion: entropy = integration of
(heat capacity)/(temperature) 
                    with respect to temperature. I am
just wondering if fpmd
                    outputs an equation for entropy or
the heat capacity is
                    actually calculated somewhere.

      5) Does anyone have any suggestions on
optimizing dt, emass, 
          ecutwfc, ecutrho and (if needed)
emass_cutoff for sodium
          containing ionic solids?  I'm using NCPP
with NLCCs (PZ LDAs
          available on pwscf.org).

   Other information: I am using espresso 2.1.3 and
below is a sample of one of my input files.

       A big thank you in advance to everyone!

               Matt
                 Small

&CONTROL
  calculation ='vc-md'
  restart_mode='from_scratch'
  nstep=10
  iprint=10
  isave=10
  tstress=.TRUE.
  tprnfor=.TRUE.
  dt = 10.0 
  ndr=52
  ndw=52
  outdir
='/home/shorej/espresso/espresso-2.1.3/Frank/NaCl/'
  prefix = 'fpmd1'
  pseudo_dir =
'/home/shorej/espresso/espresso-2.1.3/pseudo/'
  ekin_conv_thr = 1.D-5
  etot_conv_thr = 1.D-5
  forc_conv_thr = 1.D-4
/
&SYSTEM
  ibrav= 0 
  celldm(1) = 10.6591128 
  nat=2, 
  ntyp=2,
  nbnd = 6 
  nelec= 12 
  ecutwfc = 40.0
  occupations = 'fixed'
  xc_type = 'PZ'
/
&ELECTRONS
  ortho_max = 100
  emass = 400.d0
  emass_cutoff = 2.5
  electron_temperature = 'not_controlled'
/
&IONS
  ion_temperature ='not_controlled'
  ion_dynamics = 'verlet'
  tempw =298.15
  tolp = 10
/
&CELL
  cell_dynamics ='pr'
  press = .000101325
  temph = 300
  wmass = 2921.28 
/
ATOMIC_SPECIES
  Na 22.99 Na.pz-n-vbc.UPF 
  Cl 35.45 Cl.pz-bhs.UPF 
ATOMIC_POSITIONS (crystal)
  Cl 0.5 0.5 0.5
  Na 0 0 0
CELL_PARAMETERS (cubic)
  10.6591128 0.00000000 0.0000000
  0.00000000 10.6591128 0.00000000
  0.00000000 0.00000000 10.6591128 


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