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This file describes the units associated with many of the key variables and equations used inside the LAMMPS code. Units used for input command parameters are described in the input_commands file. The input command "units" selects between conventional and Lennard-Jones units. See the force_fields file for more information on units for the force field parameters that are input from data files.
Conventional units:
distance = Angstroms
time = femtoseconds
mass = grams/mole
temperature = degrees K
pressure = atmospheres
energy = Kcal/mole
velocity = Angstroms/femtosecond
force = grams/mole * Angstroms/femtosecond^2
charge = +/- 1.0 is proton/electron
LJ reduced units:
distance = sigmas
time = reduced LJ tau
mass = ratio to unitless 1.0
temperature = reduced LJ temp
pressure = reduced LJ pressure
energy = epsilons
velocity = sigmas/tau
force = reduced LJ force (sigmas/tau^2)
charge = ratio to unitless 1.0
This listing of variables assumes conventional units; to convert to LJ reduced units, simply substitute the appropriate term from the list above. E.g. x is in sigmas in LJ units. Per-mole in any of the units simply means for 6.023 x 10^23 atoms.
Meaning Variable Units positions x Angstroms velocities v Angstroms / click (see below) forces f Kcal / (mole - Angstrom) masses mass gram / mole charges q electron units (-1 for an electron) (1 e.u. = 1.602 x 10^-19 coul) time --- clicks (1 click = 48.88821 fmsec) timestep dt clicks input timestep dt_in fmsec time convert dtfactor 48.88821 fmsec / click temperature t_current degrees K t_start t_stop input damping t_freq_in inverse fmsec internal temp t_freq inverse clicks damping dielec const dielectric 1.0 (unitless) Boltmann const boltz 0.001987191 Kcal / (mole - degree K) virial virial[xyz] Kcal/mole = r dot F pressure factor pfactor 68589.796 (convert internal to atmospheres) internal p_current Kcal / (mole - Angs^3) pressure p_start p_stop input press p_start_in atmospheres p_stop_in output press log file atmospheres input damping p_freq_in inverse time internal press p_freq inverse clicks damping pot eng e_potential Kcal/mole kin eng e_kinetic Kcal/mole eng convert efactor 332.0636 (Kcal - Ang) / (q^2 - mole) (convert Coulomb eng to Kcal/mole) LJ coeffs lja,ljb Kcal-Angs^(6,12)/mole bond various see force_fields file parameters 2,3,4-body terms
来源:https://docs.lammps.org/99/units.html
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