On Thursday, February 5, 2015, Rudolf Weeber <
address@hidden> wrote:
Hi,
I defined an angle_harmonic potential and a tabulated angle potential which both have a minimum at pi/3.
Then I place three particles, such they form a triangle with 3 equal sides and add a bond.
Now, the angle_harmonic bond and I seem to agree that the angle is pi/3 and the resulting energy 0.
The tabulated potential, on the other hand returns the value for 2 pi /3.
Could someone give me a hint?
Test script
setmd box_l 650 350 5
inter 0 tabulated angle "angle-45.tab"
inter 1 angle_harmonic 45 1.0471975512
part 0 pos 0.5 0.0 0
part 601 pos 0.0 0.866025403784 0
part 602 pos 1.0 0.866025403784 0
part 602 bond 1 601 0
part 602 bond 0 601 0
puts [analyze energy]
# Compute angle manually
puts "[expr acos([vecdot_product [vecsub [part 0 print pos] [part 602 print pos]] [vecsub [part 601 print pos ] [part 602 print pos ]]])]"
Excerpt from the tabulated potential (python script to generate it is attached):
#100000 0 3.14159265359
0.0 100000000000 100000000000
3.14162406983e-05 785378.528267 479.720560227
6.28324813966e-05 392683.373382 445.515858152
9.42487220949e-05 261784.988303 425.50769733
0.000125664962793 196335.795675 411.311896355
0.000157081203492 157066.280027 400.300943752
0.00018849744419 130886.60287 391.304475844
0.000219913684888 112186.833421 383.698185004
0.000251329925586 98162.0062906 377.109415213
[...]
1.04713471872 0.00282746167302 1.77656433499e-07
1.04716613496 0.00141373083269 4.44141055754e-08
1.0471975512 -0.0 -0.0
1.04722896744 -0.00141373083175 4.44141000816e-08
1.04726038368 -0.0028274616654 1.77656422301e-07
1.04729179992 -0.00424119250286 3.99726966839e-07
[...]
3.14149840487 -1047163.51675 1838.84811708
3.14152982111 -1570757.05654 1918.88224091
3.14156123735 -3141537.67556 2055.70252971
0.0 -100000000000 100000000000
Thanks in advance!
Regards, Rudolf