In manual, I have found that the coul/cut style computes the standard Coulombic interaction potential given by E = Cqiqj/(epsilon*r). where C is an energy-conversion constant, and epsilon is the dielectric constant which can be set by the dielectric command (the constant is unitless). I want to know the value and unit of C.

In the mail list, I have found a mail talking about how lammps deals with C. however, the exact value isn’t shown. I need the value and unit of C for some analysis.

In manual, I have found that the coul/cut style computes the standard
Coulombic interaction potential given by E = C*qi*qj/(epsilon*r). where C is
an energy-conversion constant, and epsilon is the dielectric constant which
can be set by the dielectric command (the constant is unitless). I want to
know the value and unit of C.

In the mail list, I have found a mail talking about how lammps deals with C.
however, the exact value isn’t shown. I need the value and unit of C for
some analysis.

you can look this up in any text book describing Coulomb's law. C
stands for 1.0/(4*pi*epsilon_0), with epsilon_0 being the dielectric
permittivity.
in the unit and value of C in LAMMPS depends on your choice of units,
of course. the value LAMMPS uses for each set of units is assigned in
the function Update::set_units() in the file update.cpp