Page Menu
Home
c4science
Search
Configure Global Search
Log In
Files
F68672447
units.html
No One
Temporary
Actions
Download File
Edit File
Delete File
View Transforms
Subscribe
Mute Notifications
Award Token
Subscribers
None
File Metadata
Details
File Info
Storage
Attached
Created
Fri, Jun 28, 10:41
Size
3 KB
Mime Type
text/html
Expires
Sun, Jun 30, 10:41 (2 d)
Engine
blob
Format
Raw Data
Handle
18459456
Attached To
rLAMMPS lammps
units.html
View Options
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<META
NAME=
"Generator"
CONTENT=
"Cosmo Create 1.0.3"
>
</HEAD>
<BODY>
<H2>
LAMMPS Units
</H2>
<P>
<A
HREF=
"README.html"
>
Return
</A>
to top-level LAMMPS documentation.
</P>
<P>
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 or input scripts.
</P>
<P>
Conventional units:
</P>
<UL>
<LI>
distance = Angstroms
<LI>
time = femtoseconds
<LI>
mass = grams/mole
<LI>
temperature = degrees K
<LI>
pressure = atmospheres
<LI>
energy = Kcal/mole
<LI>
velocity = Angstroms/femtosecond
<LI>
force = grams/mole * Angstroms/femtosecond^2
<LI>
charge = +/- 1.0 is proton/electron
</UL>
<P>
LJ reduced units:
</P>
<UL>
<LI>
distance = sigmas
<LI>
time = reduced LJ tau
<LI>
mass = ratio to unitless 1.0
<LI>
temperature = reduced LJ temp
<LI>
pressure = reduced LJ pressure
<LI>
energy = epsilons
<LI>
velocity = sigmas/tau
<LI>
force = reduced LJ force (sigmas/tau^2)
<LI>
charge = ratio to unitless 1.0
</UL>
<HR>
<P>
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.
</P>
<P>
</P>
<PRE>
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
</PRE>
</BODY>
</HTML>
Event Timeline
Log In to Comment