compute group/group command

Hi ,

I am using this command to calculate the energy of interaction between two different groups ( polymer and substrate),

group polymer type 1

region 1 block INF INF INF INF 0.0 1.5 units box
group substratelow region 1

compute adhesionlow polymer group/group substratelow

thermo_style custom step temp c_TempPoly etotal c_adhesionlow c_adhesionup c_ti v_energyps v_eps

the calculated value i output via thermo command shows something like -0.04 which is very low for interaction of a few thousand atoms. The document page says that what is calculated is total energy thus I am suspecting some kinda of an error which i couldnt find within the source

Regards
MM

Hi ,

I am using this command to calculate the energy of interaction between two
different groups ( polymer and substrate),

group polymer type 1

region 1 block INF INF INF INF 0.0 1.5 units box
group substratelow region 1
....

compute adhesionlow polymer group/group substratelow
....
thermo_style custom step temp c_TempPoly etotal c_adhesionlow
c_adhesionup c_ti v_energyps v_eps

the calculated value i output via thermo command shows something like -0.04
which is very low for interaction of a few thousand atoms. The document page
says that what is calculated is total energy thus I am suspecting some kinda
of an error which i couldnt find within the source

if you suspect an error in the code, i would suggest you first build
a very simple input with only a handful of atoms that allows to
test your hypothesis. i personally consider this very unlikely though.
more likely is that your input script selects atoms in a way that
you don't expect or that your estimate for the group/group energy
is plain wrong.

cheers,
     axel.

The thermo output command has options to normalize
extensive values (which the output of compute group/group is)
by N = # of atoms. Do you know whether that is the
case with -0.04?

Steve

Hi,

It seems I am normalizing the output, now i am getting expected results from the calculation.
Thnx for the tip.

MM