From 05308433bb4c8d5f2bb1bd9b385979d4dff15122 Mon Sep 17 00:00:00 2001 From: sjplimp Date: Tue, 18 Mar 2008 23:27:40 +0000 Subject: [PATCH] git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@1632 f3b2605a-c512-4ea7-a41b-209d697bcdaa --- doc/fix_press_berendsen.html | 21 +++++++++++---------- doc/fix_press_berendsen.txt | 21 +++++++++++---------- 2 files changed, 22 insertions(+), 20 deletions(-) diff --git a/doc/fix_press_berendsen.html b/doc/fix_press_berendsen.html index ee46d1fa1c..fe8df61d2c 100644 --- a/doc/fix_press_berendsen.html +++ b/doc/fix_press_berendsen.html @@ -125,16 +125,17 @@ fmsec or psec - see the units 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 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.

diff --git a/doc/fix_press_berendsen.txt b/doc/fix_press_berendsen.txt index 0244c14cf3..051d1d6e24 100644 --- a/doc/fix_press_berendsen.txt +++ b/doc/fix_press_berendsen.txt @@ -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