# Bond coefficient

### ### ### ### Dear All,

i want to use bond style harmonic. but i don’t know the value of r. in LAMMPS site says that : r = distance (computed by LAMMPS)

what it means that r = distance (computed by LAMMPS) ? so, how to get it?

#### (1) harmonic

``````  E = K (r - r0)^2

standard harmonic spring

r = distance (computed by LAMMPS)

coeff1 = K (energy/distance^2)  (the usual 1/2 is included in the K)
coeff2 = r0 (distance)

``````

Dear All,
i want to use bond style harmonic. but i don't know the value of r. in
LAMMPS site says that : r = distance (computed by LAMMPS)

o dear. is today the "i don't know anything about MD but do it anyway" day??

what it means that r = distance (computed by LAMMPS) ? so, how to get it?

it is what it says. the bond length, i.e. the distance between the two atoms
that forma a bond. you don't have to get it. LAMMPS computes it,
JUST AS THE MANUAL SAYS!.

please have a proper look in a text book about MD and classical force
field and only try using LAMMPS again, *after* you have understood it.

anything else will just be a waste of your time. classical MD
uses simple models, but that doesn't mean that is easy to do
it without understanding them. in practice it needs background
knowledge just like any research activity.

axel.