The "CONSTRAINT FAILURE" error in QM/MM CPMD

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Dear all nwchem users:
    I am a new nwchem user. I want to use the pspw module to do the QM/MM CPMD. There is a very useful example(CCl4+64H2O) in (http://www.nwchem-sw.org/images/Ccl4-64water.nw). I followed this example and run another small test(CO2+20H2O). The structure is produced by Gromacs. I use the shake constrain to restain water in MD simulation. But I encoutered a problem: CONSTRAINT FAILURE. My input file is:

title "CO2 + water20 - 63 atom cell"

start CO2

scratch_dir ./co2_20water
permanent_dir ./perm

memory stack 10000 mb heap 10000 mb global 20000 mb

charge 0

geometry units angstrom nocenter noautosym noautoz print xyz
C 22.74000 16.83000 22.58000
O 23.46000 16.10000 21.20000
O 21.88000 17.66000 23.84000
O 25.43000 12.88000 24.11000
H 24.97000 12.09000 23.72000
H 25.70000 12.68000 25.05000
O 22.62000 14.35000 27.10000
H 22.50000 14.76000 28.00000
H 23.22000 14.93000 26.55000
O 20.22000 20.44000 29.53000
H 20.47000 19.48000 29.37000
H 20.54000 20.71000 30.44000
O 17.89000 11.49000 28.26000
H 17.13000 11.77000 28.86000
H 17.83000 10.51000 28.08000
O 19.51000 23.54000 15.94000
H 18.77000 22.91000 16.16000
H 19.58000 24.24000 16.66000
O 18.14000 7.69000 21.53000
H 18.31000 6.96000 22.19000
H 18.64000 8.51000 21.80000
O 25.85000 10.62000 14.53000
H 26.83000 10.48000 14.67000
H 25.57000 10.15000 13.69000
O 18.22000 5.75000 23.46000
H 17.29000 5.51000 23.73000
H 18.87000 5.28000 24.06000
O 25.00000 8.45000 32.01000
H 25.94000 8.63000 32.31000
H 24.39000 8.45000 32.80000
O 16.01000 7.86000 30.01000
H 16.76000 8.45000 30.32000
H 16.28000 7.39000 29.17000
O 31.03000 7.58000 17.12000
H 30.29000 7.35000 16.49000
H 30.85000 8.47000 17.54000
O 19.63000 19.49000 9.40000
H 19.69000 20.31000 8.83000
H 18.85000 19.56000 10.01000
O 11.36000 11.37000 16.27000
H 11.78000 10.75000 15.61000
H 10.48000 11.69000 15.93000
O 20.07000 25.48000 11.68000
H 20.45000 25.35000 12.60000
H 20.19000 24.64000 11.15000
O 8.50000 19.55000 22.34000
H 8.53000 18.57000 22.55000
H 8.45000 20.08000 23.19000
O 14.40000 6.31000 16.90000
H 13.59000 5.96000 16.43000
H 14.30000 6.15000 17.88000
O 22.32000 2.70000 28.18000
H 22.87000 3.03000 27.41000
H 22.88000 2.67000 29.00000
O 37.82000 16.60000 19.17000
H 38.26000 17.35000 18.66000
H 37.05000 16.96000 19.70000
O 15.96000 25.91000 33.36000
H 16.62000 25.17000 33.28000
H 15.76000 26.28000 32.45000
O 7.73000 20.71000 24.70000
H 7.76000 21.70000 24.60000
H 7.83000 20.46000 25.66000
end

NWPW
  QMMM
mm_tags 4:63
lj_ion_parameters C 2.95000000d0 0.1266700d0
lj_ion_parameters O 3.83000000d0 0.0136200d0
lj_ion_parameters O^ 3.16555789d0 0.15539425d0

     # new input format
fragment spc
size 3
index_start 4:61:3

        #spc/e water
shake units angstroms 1 2 3 cyclic 1.0 1.632993125 1.0
end

  END
END


            • Setup conjugate gradient code ****
nwpw
  SIMULATION_CELL
SC 10.00
END
xc pbe96
mult 2
lmbfgs
#translation on
end
task pspw gradient


nwpw
  car-parrinello
Nose-Hoover 1410.0 300.0 1410.0 300.0 clear
time_step 5.00
fake_mass 750.0
loop 5 500
scaling 1.00 1.00
end
end
task pspw car-parrinello

Can anyone give a help for me? I will be greatly appreciated!


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