Error of PPPM

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1

Hi, all, there is a problem I am facing for one month. I am using CVFF to simulate my system. While the input include the electrostatic force, it is hard to minimize the energy of the system, the final energy is negative.

and there are errors when I fix system in NPT, as

out of range cannot compute PPPM.

I try to use neighbor modify to fix that, however, it did not work.

I am not sure it is because the structure issue or the coefficients for the input.

here is the input for my job:

units real
dimension 3
boundary p p p

atom_style full # include charges
pair_style lj/cut/coul/long 12 # only Lennard-Jones potential
bond_style harmonic
angle_style harmonic
dihedral_style harmonic
improper_style cvff

read_data CNTket_1.dat

kspace_style pppm 1e-6
#kspace_style none
special_bonds lj 0.0 0.0 1.0 coul 0 0 1
#newton on off

bond_coeff 2 372.4000 1.3730
angle_coeff 5 63.3100 119.9500
angle_coeff 10 63.0300 118.5800
improper_coeff 5 0.4000 -1 2

Thanks,
Haoxiang Huang

2

2015年7月4日 下午9:11於 “Huang, Haoxiang” <hcwong@…123…>寫道：

Hi, all, there is a problem I am facing for one month. I am using CVFF to simulate my system. While the input include the electrostatic force, it is hard to minimize the energy of the system, the final energy is negative.

and there are errors when I fix system in NPT, as

out of range cannot compute PPPM.

This is a commonly discussed error on the mailing list. Please run a search and you can find plenty discussions.

I try to use neighbor modify to fix that, however, it did not work.

I am not sure it is because the structure issue or the coefficients for the input.

Nobody can tell without the structure file and such limited information. And what is wrong with negative energy?

Ray

3

After I test some cases: I found it was weird that, when I defined the special bonds, it was fine for lj 0 0 1 but coul 0 0 1 did not work. If I define both of them, the system will miss one bonding at the beginning of simulation. Minimizing energy may not the issue for this case. Since the net charge of the system is not zero, I am not sure it is the correct way to define the special bonds like that.