Re: [ESPResSo-users] Angle potentials seem to disagree about the angle between particles

[Axel Arnold]

Hi!

The code for tabulated indeed puts the zero position opposite to the normal 
angle potential, for whatever reason. Karen however implemented a fix long ago, 
you just need to define TABANGLEMINUS to get the same behavior. Just changing 
the default behavior would however break other scripts, so we should probably 
leave that inconsistency till we switch to Python and a new interface, where we 
can break any conventions.

Best,
Axel

> On 05.02.2015, at 17:04, 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
> 
> <gen-tabualted-angle.py>

------------------------------------------------
JP Dr. Axel Arnold
ICP, Universität Stuttgart
Allmandring 3
70569 Stuttgart, Germany
Email: address@hidden
Phone: +49 711 685 67609