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[Ravinder Abrol <rabrol@us.ibm.com>]

Dear Michel,

Thanks for your acell observation. I
mistakenly assumed that
the cell length was in angstrom units.
Increasing it worked and
the naphthalene is planar now.

Thanks very much!
Ravi

-----
Ravinder  Abrol,  Ph. D.
25-143, Department of Physical Sciences
IBM Thomas J. Watson Research Center
Yorktown Heights, NY 10598
Phone: 914-945-1617
Email: rabrol@us.ibm.com

"Cote Michel" <michel.cote@umontreal.ca>

03/31/2004 05:38 PM

Please respond to
forum

To	<forum@abinit.org>
cc
Subject	RE: [abinit-forum] molecular crystals...

Dear Ravi,

I did molecular crystals of naphthalene and pentacene with abinit and I
had no problem. For your naphthalene calculations, looking at your input
it seems that your box in to small. The molecule extent from about -3 to
3 Angstroms, which is roughly 11 bohr but your box is only 12 bohr. So
your naphthalene molecule interacts with its periodic images! Increase
your box size and that should fix your problem. 

Also, don't expect to get the right lattice parameters with DFT. Since
DFT does not include van der Waals interactions, at the moment, the calculated
lattice parameters are quite off from the experimental values. 

I hope it helps.

Michel

*************************************************************** 
  Michel Cote                
         tel: +1 (514) 343-5628    
  Professeur adjoint              
    fax: +1 (514) 343-2071          
    
  Département de physique
  Université de Montréal
  C.P. 6128, succ. Centre-ville
  Montréal (Québec) H3C 3J7          Michel.Cote@umontreal.ca
  Canada              http://www.phys.umontreal.ca/~michel_cote
***************************************************************
  
  
                    
     
 

> -----Message d'origine-----
> De : rabrol@us.ibm.com [mailto:rabrol@us.ibm.com]
> Envoyé : 31 mars, 2004 16:43
> À : forum@abinit.org
> Objet : [abinit-forum] molecular crystals...
> 
> 
> Hi All,
> I am starting to use AbInit and have finished all the
> tutorials. I want to study molecular crystals like
> naphthalene, pentacene.
> Does anybody have some idea about how good the GGA
> exchange-correlation functionals like PBE or RPBE
> are for these van der Waals crystals?
> 
> I tried using RPBE GGA functional for geometry optimization
> of a single naphthalene molecule and the minimum energy
> structure came out to be non-planar. The ground state
> geometry being planar, do I need to use any constraints to keep
> the molecule planar or I am doing something wrong.
> Here's my input file:
> 
> -----------------------start of input file---------------------
> # Single naphthalene molecule
> #
> # Geometry optimisation
> 
> # RPBE GGA functional
> ixc  15
> 
> ndtset 1
> 
> # geometry optimization
> ionmov 2
> ntime 20
> tolmxf 5.0d-4
> nband 24
> 
> #Definition of the planewave basis set
> ecut 30.0         # Maximal kinetic energy cut-off,
in Hartree
> 
> toldfe  1.0d-6
> 
> #Definition of the unit cell
> acell 12 12 12
> 
> #Definition of the atom types
> ntypat 2          # There are two types of
atoms
> 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 types 
> are carbon and hydrogen
>  
> 
> #Definition of the atoms
> natom 18          # There are 18 atoms in
1 naphthalene molecule
> typat 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 1
>              # They are of type
1 or 2, that is, carbon or 
> hydrogen respectively
> xangst       # This keyword indicate that the location
of the atoms
>              # will follow, one
triplet of number for each atom
>     0.51156     1.49914    -1.00626
>     0.94747     2.32584    -0.85293
>     0.08820     1.13232    -2.26318
>     0.22250     1.75733    -3.01875
>    -0.55004    -0.11049    -2.46435
>    -0.82988    -0.35063    -3.37189
>    -0.75471    -0.97534    -1.41169
>    -1.19403    -1.81924    -1.52799
>    -0.51156    -1.49914     1.00626
>    -0.94747    -2.32584     0.85293
>    -0.08820    -1.13232     2.26318
>    -0.22250    -1.75733     3.01875
>     0.55004     0.11049     2.46435
>     0.82988     0.35063     3.37189
>     0.75471     0.97534     1.41169
>     1.19403     1.81924     1.52799
>     0.32066     0.62614     0.10178
>    -0.32066    -0.62614    -0.10178
> 
> 
> #Definition of the SCF procedure
> nstep 20          # Maximal number of SCF
cycles
> diemac 2.0
> --------------------------end of input file-----
> 
> Any help is greatly appreciated.
> Thanks,
> Ravi
>