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Re: [lammps-users] fix heat command
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Re: [lammps-users] fix heat command


From: "Crozier, Paul S" <pscrozi@...3...>
Date: Fri, 24 Jul 2009 08:24:47 -0600

eflux is input and is extensive

escale is output and is intensive

Paul

________________________________________
From: Steve Plimpton [sjplimp@...24...]
Sent: Friday, July 24, 2009 8:07 AM
To: Crozier, Paul S
Cc: German Samolyuk; lammps-users@lists.sourceforge.net
Subject: Re: [lammps-users] fix heat command

Paul - I don't understand.  Is the output (not input eflux) of the fix
intensive or extensive.  It's the sqrt of this quantity

double escale = (ke + heat - 0.5*vcmsq*masstotal)/(ke - 0.5*vcmsq*masstotal);

which looks intensive, and the output routines are treating it as such.

Steve

On Thu, Jul 23, 2009 at 11:20 AM, Crozier, Paul S<pscrozi@...3...> wrote:
> From the documentation (http://lammps.sandia.gov/doc/fix_heat.html): "The eflux parameter determines the change in aggregate energy of the entire group of atoms."  So the energy specified by the user is the total energy subtracted/added from the group. (Since it is energy/time, it is really a power rather than an energy.)  Since the value specified by the user would need to scale with the number of atoms in the group in order to achieve the same per-atom heating, the eflux parameter is an extensive rather than an intensive property. I think that there is no inconsistency with the rest of LAMMPS.
>
> Paul
>
>> -----Original Message-----
>> From: Steve Plimpton [mailto:sjplimp@...24...]
>> Sent: Thursday, July 23, 2009 8:24 AM
>> To: German Samolyuk
>> Cc: lammps-users@lists.sourceforge.net; Crozier, Paul S
>> Subject: Re: [lammps-users] fix heat command
>>
>> Looking at the code for fix_heat.cpp, it's normalized
>> by # of atoms in the group.
>>
>> As far as I recall, all other intensive quantities output
>> by LAMMPS (thermo, fixes, etc) are normalized
>> by the total # of atoms in the system, not by the
>> # in the group.
>>
>> So I need to ask Paul about this.  Paul, does this
>> seem inconsistent - or is it a requirement of fix heat
>> since it needs Vcm?
>>
>> Steve
>>
>> On Wed, Jul 22, 2009 at 9:10 AM, German Samolyuk<samolyuk@...24...>
>> wrote:
>> > Dear lammps users,
>> >
>> > Is the "eflux" value in  fix heat command "fix ID group-ID heat N
>> > eflux" energy/time units per each atom in group-ID or per all  atoms
>> > in the group-ID
>> >
>> > Thank you,
>> >
>> > German Samolyuk
>> >
>> > ---------------------------------------------------------------------
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>
>
>