[Pw_forum] constraints

[ali kazempour]

Dear All
I want to fix the distance between  two atom during relaxation , the distance is 1.98 , but the code crash and the error is 
     target =   3.67419827
     dmax   =   2.79062000

 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
     from init_constraint : error #         1
     the target for constraint 1 is larger than the largest possible value
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

why does it happen and what can I do?


this is my input file:

 &CONTROL
                       title = 'routile lattice BFGS' ,
                 calculation = 'relax' ,
                restart_mode = 'from_scratch' ,
                      outdir = '/ptmp/kazempou/scratch' ,
                  pseudo_dir = './' ,
                      prefix = 'routil lattice default' ,
               etot_conv_thr = 0.000000735 ,
               forc_conv_thr = 0.0011668141375 ,
 /
 &SYSTEM
                       ibrav = 6,
                   celldm(1) = 8.68,
                   celldm(3) = 0.643,
                         nat = 6,
                        ntyp = 2,
                     ecutwfc = 15 ,
                     ecutrho = 400 ,
 /
 &ELECTRONS
                    conv_thr = 1.0D-4 ,
 /
 &IONS
 /
ATOMIC_SPECIES
   Ti   47.86700  ti.optgga2.fhi.UPF 
    O   15.99940  o.optgga1.fhi.UPF 
ATOMIC_POSITIONS crystal 
   Ti      0.000000000    0.000000000    0.000000000    
   Ti      0.500000000    0.500000000    0.500000000    
    O      0.305300000    0.305300000    0.000000000    
    O     -0.305300000   -0.305300000    0.000000000    
    O      0.805300000    0.194700000    0.500000000    
    O      0.194700000    0.805300000    0.500000000    
K_POINTS automatic 
  8 8 10   0 0 0 
CONSTRAINTS
  1  1.98 
  'distance'      2   4 

thanks a lot


 Ali Kazempour





Fritz-Haber-Institut              fax   : ++49-30-8413 4701
der Max-Planck-Gesellschaft
Faradayweg 4-6                    e-mail: kazempou at fhi-berlin.mpg.de
D-14 195 Berlin-Dahlem / German



      
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