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git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@1632 f3b2605a-c512-4ea7-a41b-209d697bcdaa

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sjplimp 2008-03-18 23:27:40 +00:00
parent be95828466
commit 05308433bb
2 changed files with 22 additions and 20 deletions
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21
doc/fix_press_berendsen.html
View File

@ -125,16 +125,17 @@ fmsec or psec - see the <A HREF = "units.html">units</A> command).
bulk modulus of the system (inverse of isothermal compressibility).
The bulk modulus has units of pressure and is the amount of pressure
that would need to be applied (isotropically) to reduce the volume of
the system by a factor of 2. The bulk modulus can be set via the
keyword <I>modulus</I>. The <I>Pdamp</I> parameter is effectively multiplied by
the bulk modulus, so if the pressure is relaxing faster than expected
or desired, increasing the bulk modulus has the same effect as
increasing <I>Pdamp</I>. The converse is also true. LAMMPS does not
attempt to guess a correct value of the bulk modulus; it just uses
10.0 as a default value which is about right for a Lennard-Jones
liquid, but will be way off for other materials and way too small for
solids. Thus you should experiment to find appropriate values of
<I>Pdamp</I> and/or the <I>modulus</I> when using this fix.
the system by a factor of 2 (assuming the bulk modulus was a constant,
independent of density, which it's not). The bulk modulus can be set
via the keyword <I>modulus</I>. The <I>Pdamp</I> parameter is effectively
multiplied by the bulk modulus, so if the pressure is relaxing faster
than expected or desired, increasing the bulk modulus has the same
effect as increasing <I>Pdamp</I>. The converse is also true. LAMMPS does
not attempt to guess a correct value of the bulk modulus; it just uses
10.0 as a default value which gives reasonable relaxation for a
Lennard-Jones liquid, but will be way off for other materials and way
too small for solids. Thus you should experiment to find appropriate
values of <I>Pdamp</I> and/or the <I>modulus</I> when using this fix.
</P>
<HR>

21
doc/fix_press_berendsen.txt
View File

@ -116,16 +116,17 @@ IMPORTANT NOTE: The relaxation time is actually also a function of the
bulk modulus of the system (inverse of isothermal compressibility).
The bulk modulus has units of pressure and is the amount of pressure
that would need to be applied (isotropically) to reduce the volume of
the system by a factor of 2. The bulk modulus can be set via the
keyword {modulus}. The {Pdamp} parameter is effectively multiplied by
the bulk modulus, so if the pressure is relaxing faster than expected
or desired, increasing the bulk modulus has the same effect as
increasing {Pdamp}. The converse is also true. LAMMPS does not
attempt to guess a correct value of the bulk modulus; it just uses
10.0 as a default value which is about right for a Lennard-Jones
liquid, but will be way off for other materials and way too small for
solids. Thus you should experiment to find appropriate values of
{Pdamp} and/or the {modulus} when using this fix.
the system by a factor of 2 (assuming the bulk modulus was a constant,
independent of density, which it's not). The bulk modulus can be set
via the keyword {modulus}. The {Pdamp} parameter is effectively
multiplied by the bulk modulus, so if the pressure is relaxing faster
than expected or desired, increasing the bulk modulus has the same
effect as increasing {Pdamp}. The converse is also true. LAMMPS does
not attempt to guess a correct value of the bulk modulus; it just uses
10.0 as a default value which gives reasonable relaxation for a
Lennard-Jones liquid, but will be way off for other materials and way
too small for solids. Thus you should experiment to find appropriate
values of {Pdamp} and/or the {modulus} when using this fix.
:line