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[apirath@hpcc.nectec.or.th]

Hi all, 

I have a problem in determining the bond length of a Carbon dimer molecule. 
I have calculated the total-energy curve as a function of the seperation 
between C atoms, and I found that there was a "discontinuity" in the 
total-energy curve. The calculated forces were competely wrong as well. 

THIS IS MY RESULTS ---------------------------- 
distance(angstrom)  etotal(Ha)    force(Ha/Bohr) 
    1.20  -1.1651337270E+01 1.3031579214E-01 
    1.21  -1.1654900731E+01 1.3727504151E-01 
    1.22  -1.1657978193E+01 1.4365447983E-01 
    1.23  -1.1660595870E+01 1.4949382326E-01 
    1.24  -1.1662778804E+01 1.5483024408E-01 
    1.25  -1.1664550918E+01 1.5969856326E-01 
    1.26  -1.1665935074E+01 1.6413199426E-01 
    1.27  -1.1666953111E+01 1.6816076344E-01 
    1.28  -1.1667625891E+01 1.7181292372E-01 
    1.29  -1.1667973365E+01 1.7511469508E-01 
    1.30  -1.1668014577E+01 1.7808921357E-01 
    1.31  -1.1667767719E+01 1.8075753719E-01 
    1.32  -1.1667250181E+01 1.8313998960E-01 
    1.33  -1.1666478571E+01 1.8525566926E-01 
    1.34  -1.1665468752E+01 1.8712238288E-01 
    1.35  -1.1664235868E+01 1.8875757765E-01 
    1.36  -1.1662794390E+01 1.9017574862E-01 
    1.37  -1.1661158127E+01 1.9139192204E-01 
    1.38  -1.1659340222E+01 1.9241851915E-01 
    1.39  -1.1657353280E+01 1.9326725253E-01 
    1.40  -1.1655209271E+01 1.9394818125E-01 
    1.41  -1.1652919625E+01 1.9447164545E-01 
    1.42  -1.1650495230E+01 1.9484767225E-01 
    1.425 -1.1649235767E+01 1.9498321914E-01 
    1.43  -1.1647946464E+01 1.9508545971E-01 
    1.44  -1.1645283198E+01 1.9519402188E-01 
    1.444 -1.1644187951E+01 1.9520318369E-01 
    1.448 -1.1630758882E+01 6.8353016987E-02 <<=== !! Discontinous !! 
    1.45  -1.1630603864E+01 6.9325554195E-02 
    1.452 -1.1630444414E+01 7.0286281207E-02 
    1.456 -1.1630112457E+01 7.2172709473E-02 
    1.46  -1.1629763477E+01 7.4013056829E-02 
    1.47  -1.1628819530E+01 7.8416984820E-02 
-------------------------------------------- 

THIS IS MY INPUT------------------ 
the pseudopotential file = 6c.pspnc 

ndtset 15 
                                                                              
                                 
#Definition of the unit cell 
acell 40 40 40  angstrom 
                                                                              
                                 
#Definition of the atom types 
ntypat 1 
znucl 6 
                                                                              
                                 
#Definition of the atoms 
natom 2 
typat 1 1 
xangst: 
   6.00 6.0 6.0 
   7.20 6.0 6.0 
                                                                              
                                 
xangst+ 
   0.00 0.0 0.0 
   0.02 0.0 0.0 
                                                                              
                                 
#Definition of the planewave basis set 
ecut 60.0 
                                                                              
                                 
#Definition of the k-point grid 
nkpt 1 
                                                                              
                                 
#Definition of the SCF procedure 
nstep 100 
toldfe 1.0d-6 
diemac 3.0 
diemix 0.0 
---------------------------------- 
I used "ABINIT version 4.3.3" compiled by intel compiler "efc" with the "MKL 
library". 
This run on "Itanium2" and OS is "Linux".   

Could anyone please check the result and tell me what's wrong with this 
calculation. 

Thank you, 
Apirath