Hello everyone,
I have some questions related to the energy term of compute bond/local and angle/local.
I simulated a mixture of 4000H2O+1714CH4. I used compute bond/local angle/local for bond and angle energy for H2O and CH4 group. I also output system bond and angle energy with thermo ebond and eangle. The following is my commands,
variable eb equal ebond
variable ea equal eangle
compute 1 H2O bond/local dist engpot force
compute 2 H2O reduce ave c_1[*]
compute 3 H2O angle/local theta eng
compute 4 H2O reduce ave c_3[*]
compute 5 CH4 bond/local dist engpot force
compute 6 CH4 reduce ave c_5[*]
compute 7 CH4 angle/local theta eng
compute 8 CH4 reduce ave c_7[*]
fix eb all ave/time ${Nevery} ${Nrepeat} ${Nfreq} v_eb ave window 5
fix ea all ave/time ${Nevery} ${Nrepeat} ${Nfreq} v_ea ave window 5
fix b_H2O H2O ave/time ${Nevery} ${Nrepeat} ${Nfreq} c_2[*] ave window 5 file b_H2O.txt title2 'TimeStep dist engpot force'
fix a_H2O H2O ave/time ${Nevery} ${Nrepeat} ${Nfreq} c_4[*] ave window 5 file a_H2O.txt title2 'TimeStep theta eng'
fix b_CH4 CH4 ave/time ${Nevery} ${Nrepeat} ${Nfreq} c_6[*] ave window 5 file b_CH4.txt title2 'TimeStep dist engpot force'
fix a_CH4 CH4 ave/time ${Nevery} ${Nrepeat} ${Nfreq} c_8[*] ave window 5 file a_CH4.txt title2 'TimeStep theta eng'
This is my result. Data ended with_log is from thermo eb and ea . Others are from compute local.
| eb_log | ea_log | b_H2O | a_H2O | b_CH4 | a_CH4 |
|---|---|---|---|---|---|
| 10630.452 | 9082.6596 | 0.737721 | 0.718825 | 0.689715 | 0.603594 |
My calculations of bond energy are,
4000 * b_H2O + 1714 * b_CH4 should equal to 10630.452, but I got 4133.05551.
But if I do 4000 * b_H2O * 2 (2 bonds per H2O) + 1714 * b_CH4 * 4 (4 bonds per CH4), then I got 10630.45404, very close to 10630.452.
This happens the same for angles,
4000 * a_H2O + 1714 * a_CH4 should equal to 9082.6596, but I got 3909.860116.
If I do 4000 * a_H2O + 1714 * a_CH4 * 6 (6 angles per CH4), then I got 9082.660696, very close to 9082.6596.
How should I interpret the above calculations? Especially the energy term of compute /local.
Thanks in advance.