[ESPResSo] Question about P3M and MMM2D

[Salvador Herrera Velarde]

Hi,
 
 I am interested in simulate a charged bilayer membrane. First, I need a 2D electrostatic method + NPT ensamble. If I
understood well, this is only possible with MMM2D. So, I put the center
of the bilayer as close as possible to the bottom of the simulation
box and choose and appropiete value for layered cell (>4). Then, I
need to calculate the surface tension of the membrane (I want to obtain
the tensionless state) but when I tried with stress_tensor I got the
next message:
 
 WARNING: pressure calculated, but MMM2D pressure not implemented => stress tensor of membranes
 
 Is there another way in ESPresSO to calculate the stress_tensor or the surface tension?
 
 Besides, once I know the tensionless state of the membrane, I want to use the P3M + ELC method for the same system. However,
I am not sure what is the criterion to choose the best value for the
parameter "skin". I run some test simulations in my desktop computer
 
 #P3M + ELC  skin 0.4
   background_errors 0 {001 number of cells 1 is smaller than
minimum 8 (interaction range too large or max_num_cells too small)}
 
 #P3M + ELC  skin 1.0
    {coulomb 1.55 p3m 6.562365701286867 32 6 0.4436576322607176 7.641701920650234e-5}
   {coulomb epsilon  metallic n_interpol 32768 mesh_off
0.5 0.5 0.5} {coulomb elc 0.0001 13.808598559818787 0.06611687661638957}
 
 #P3M + ELC  skin 1.5
    {coulomb 1.55 p3m 6.062365701286867 32 6 0.48136997545253307 9.22176560109132e-5}
   {coulomb epsilon  metallic n_interpol 32768 mesh_off
0.5 0.5 0.5} {coulomb elc 0.0001 13.808598559818787 0.06611687661638957}
 
 #P3M + ELC  skin 2.0
    {coulomb 1.55 p3m 5.562365701286867 32 7 0.5259642582393248 9.693819928448824e-5}
    {coulomb epsilon  metallic n_interpol 32768 mesh_off 0.5 0.5 0.5} {coulomb elc 0.0001 13.808598559818787
 
 Should I use the minimum value of skin where the system in well behaved (it does not crash)?
 any advice how should I choose this value?
 Furthermore, If I choose a specific value for the skin using MMM2D (P3M + ELC), the same value can be used for MMM2D (P3M+ELC)
  and get the same results ?
 
Sorry if these are silly questions. This is the first time that I am
trying to run simulations with long-range electrostatics interactions.
 
 Thanks a lot,
 
 Salvador