[ESPResSo-devel] Local stress tensor/Multibody interaction and A bug in tensor distribute

[Zunjing Wang]

Hi, all,

Here I have several questions on command "analyze local_stress_tensor" or "
analyze stress_tensor" for computing local/total stress tensor of an
non-isotropic system, for example, a membrane.

1) Checking with the newest released version Espresso-2.1.2j, I found that
it does not include any 3-body or higher-order interactions, eg. Angle
bending, Dihedrals. Has any Espresso developer ever coded this part? If not,
then when involving any three-body interactions, how reliable about the
results of stress tensor with current Espresso?


2) Another question is about a bug in source code:
IN FILE:   pressure.c
FUNCTION:  int distribute_tensors(DoubleList *TensorInBin, double *force,
int bins[3], double range_start[3], double range[3], double pos1[3], double
pos2[3])
LINE 757-762:
----------------------------------------------------------------------------
if (calclength - length >0.0000000001) {
      char *errtxt = runtime_error(128 + 3*TCL_INTEGER_SPACE);
      ERROR_SPRINTF(errtxt, "{%d: analyze stess_profile: bug in distribute
tensor code - calclength is %e and length is %e calclength-length is %e,
counter is %d}",this_node,calclength,length,calclength-length, counter);
      return 0;
}
----------------------------------------------------------------------------
Does anyone know that who coded this part and how this value "0.0000000001"
was decided? Will it be effected by compiler or machine? For my system, this
value "0.0000000001" sounds too small, leading to crash of Espresso when
computing local stress tensor.

Thanks in advance for any possible help,
Zunjing

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Zun-Jing WANG, Ph.D.
Dept. of Physics                      ++1-412-268-2771 (office)
Carnegie Mellon University            ++1-412-681-0648 (fax)
5000 Forbes Avenue                    ++1-412-268-2740 (Donna Thomas)
Pittsburgh, PA 15213                  address@hidden
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