The ABINIT Users Mailing List ( CLOSED )

["D. R. Hamann" <drh@bell-labs.com>]

Dear Mengbo,

Abinit can calculate the elastic tensor directly using its 
response-function capabilities.  Running abinit and then anaddb will 
correctly include atomic relaxations.  While there is not yet a tutorial 
on this (coming soon) look at Test_v4/t61-70 and the relevant README 
sections.  Also, look at the abinit input variable rfstrs and the anaddb 
input variables elaflag and instrflag.

Don Hamann

Pawel Scharoch wrote:

>   Dear Mengbo,
>
>     I have noticed that the relative atomic positions  are
>   fixed in your supercell while  you change the supercell
>   shape. Perhaps they should be allowed to relax ?
>
>    With regards,
>
>    Pawel
>
>
> On Thu, 12 May 2005 mbluo@yahoo.com.cn wrote:
>
> > Hi, Abinit members,
> >
> > I want to calculate the shear modulus of Si as an example. The input 
> > file is attached. By varying the angle, I get energy - angle relation 
> > and from which the shear modulus is determined. However, I find the 
> > shear modulus (about 104 GPa) is bigger than the bulk modulus (about 
> > 94 GPa). This is contrary to the experimental results. LDA and GGA 
> > pseudopotentials give almost the same result.
> >
> > Your help and commants are helpful. Thanks
> >
> > Mengbo Luo
> >
> > ***************************
> >
> > The Input file is:
> >
> > # Crystalline silicon : computation of the total energy
> > #  ZnS structure
> >
> > ndtset 6
> > jdtset 5 6 7 8 9 10
> >
> > chkprim 0
> >
> > #Definition of the unit cell  OPT:10.20360336
> > #  angdeg: angdeg(1) is the angle between the 2nd and 3rd vectors,
> > #          angdeg(2) is the angle between the 1st and 3rd vectors,
> > #          angdeg(3) is the angle between the 1st and 2nd vectors,
> > # 1 1 0
> >
> > acell1  2*10.20360336   10.20360336
> > angdeg1 90   90   90
> > acell2  2*10.20360336   10.20515765494
> > angdeg2 90   89   90
> > acell3  2*10.20360336   10.20982290826
> > angdeg3 90   88   90
> > acell4  2*10.20360336   10.21760623424
> > angdeg4 90   87   90
> > acell5  2*10.20360336   10.22851951947
> > angdeg5 90   86   90
> > acell6  2*10.20360336   10.24257946719
> > angdeg6 90   85   90
> > acell7  2*10.20360336   10.25980765986
> > angdeg7 90   84   90
> > acell8  2*10.20360336   10.280230640285
> > angdeg8 90   83   90
> > acell9  2*10.20360336   10.30388001197
> > angdeg9 90   82   90
> > acell10  2*10.20360336  10.33079255937
> > angdeg10 90   81   90
> >
> >
> > #Definition of the k-point grid
> > kptopt 1
> > nshiftk 1
> > shiftk 0.5 0.5 0.5
> >                 # In cartesian coordinates, this grid is simple 
> > cubic, and
> >                  # actually corresponds to the
> >                  # so-called 4x4x4 Monkhorst-Pack grid
> >
> > ngkpt  3*8
> >
> > getwfk -1
> >
> > #Definition of the atom types
> > ntype 1
> > zatnum 14
> >
> >
> > #Definition of the atoms
> > natom 8          # There are two atoms
> > type 8*1         # They both are of type 1, that is, Silicon.
> > xred
> >   0.0  0.0  0.0
> >   0.5  0.5  0.0
> >   0.0  0.5  0.5
> >   0.5  0.0  0.5
> >   0.25  0.25  0.25
> >   0.75  0.75  0.25
> >   0.25  0.75  0.75
> >   0.75  0.25  0.75
> >
> > #Definition of the planewave basis set
> > ecut  40.0
> >
> > #Definition of the SCF procedure
> > nstep 15
> > toldfe 1.0d-6
> > diemac 12.0


--
D. R. Hamann                            Phone: 908-582-4454
Director, Theoretical Materials         Fax:   908-582-4868
 Physics Research (retired)             email: drh@physics.bell-labs.com
Bell Laboratories 
Lucent Technologies
700 Mountain Ave, Room 1D-371
Murray Hill, NJ 07974-0636 USA