some questions in reax/c?

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1

Dear all
I am using reax/c during the NEMD simulation with wall/reflection.The system is RDX crystal.I have some questions about the reax/c:

  1. how to calculate the bond energy, such as C-C, C-H, C-N et al. bong energy?
    I saw the manual and found the compute bond/local command may calculate the bond energy.

compute 2 all bond/local dist engpot
dump 1 all local 1000 tmp.dump index c_2[*]

ERROR: Compute bond/local used when bonds are not allowed.

How to modify it？

  1. how to subtract the center-of-mass velocity?

compute myTemp all temp/com
compute RDXX hot chunk/atom bin/2d x 0 5 y 0 5 units box

fix 6 hot ave/chunk 100 1 1000 RDXX vx vy vz temp density/mass bias myTemp norm sample file tmp_RDX.out

The temp in fix command is the real temperature, is it right?

  1. how to calculate the real press?

In lammps, the press is computed by the formula

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compute peratom hot stress/atom NULL
variable meanpress1 atom -(c_peratom[1]+c_peratom[2]+c_peratom[3])/3

fix 7 hot ave/chunk 100 1 1000 RDXX v_meanpress1 norm sample file tmp_RDX_press.out

Is the v_meanpress1 in fix command the real press?

2

Hello, I also use ReaxFF potential file.

Question 1. You need to make particular program to analyze bond energy in ReaxFF. As far as I know, LAMMPS can not obtain such data by its integrated commands.

Question 2. Please check “fix momentum” command.

Question 3. Please check “compute stress/atom” command in manual. There is an example to calculate the pressure you want.

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3

Compute bond/local works for models with fixed explicit bond topology,

e.g. see the bond_style command. ReaxFF (and other bond-order

potentials) have implicit bonds.

Steve

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