2010-06-22 22:52:12 +08:00
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<HTML>
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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
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<HR>
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<H3>fix adapt command
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</H3>
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<P><B>Syntax:</B>
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</P>
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2010-10-23 05:24:19 +08:00
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<PRE>fix ID group-ID adapt N attribute args ... keyword value ...
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2010-06-22 22:52:12 +08:00
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
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<LI>adapt = style name of this fix command
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<LI>N = adapt simulation settings every this many timesteps
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2010-10-23 05:24:19 +08:00
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<LI>one or more attribute/arg pairs may be appended
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2010-06-22 22:52:12 +08:00
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2010-10-23 05:24:19 +08:00
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<LI>attribute = <I>pair</I> or <I>kspace</I> or <I>atom</I>
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2010-06-22 22:52:12 +08:00
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2010-08-13 07:10:38 +08:00
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<PRE> <I>pair</I> args = pstyle pparam I J v_name
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2010-06-22 22:52:12 +08:00
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pstyle = pair style name, e.g. lj/cut
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pparam = parameter to adapt over time
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I,J = type pair(s) to set parameter for
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2010-08-13 07:10:38 +08:00
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v_name = variable with name that calculates value of pparam
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2010-10-23 05:24:19 +08:00
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<I>kspace</I> arg = v_name
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v_name = variable with name that calculates scale factor on K-space terms
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2010-08-13 07:10:38 +08:00
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<I>atom</I> args = aparam v_name
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2010-06-22 22:52:12 +08:00
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aparam = parameter to adapt over time
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2010-08-13 07:10:38 +08:00
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v_name = variable with name that calculates value of aparam
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2010-06-22 22:52:12 +08:00
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</PRE>
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2010-10-23 05:24:19 +08:00
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<LI>zero or more keyword/value pairs may be appended
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<LI>keyword = <I>scale</I> or <I>reset</I>
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<PRE> <I>scale</I> value = <I>no</I> or <I>yes</I>
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<I>no</I> = the variable value is the new setting
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<I>yes</I> = the variable value multiplies the original setting
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</PRE>
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<PRE> <I>reset</I> value = <I>no</I> or <I>yes</I>
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<I>no</I> = values will remain altered at the end of a run
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<I>yes</I> = reset altered values to their original values at the end of a run
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</PRE>
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2010-06-22 22:52:12 +08:00
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</UL>
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<P><B>Examples:</B>
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</P>
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2010-08-13 07:10:38 +08:00
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<PRE>fix 1 all adapt 1 pair soft a 1 1 v_prefactor
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fix 1 all adapt 1 pair soft a 2* 3 v_prefactor
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2011-05-18 07:43:48 +08:00
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fix 1 all adapt 1 pair lj/cut epsilon * * v_scale1 coul/cut scale 3 3 v_scale2 scale yes reset yes
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2010-08-13 07:10:38 +08:00
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fix 1 all adapt 10 atom diameter v_size
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2010-06-22 22:52:12 +08:00
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</PRE>
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<P><B>Description:</B>
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</P>
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2010-10-23 05:24:19 +08:00
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<P>Change or adapt one or more specific simulation attributes or settings
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over time as a simulation runs. Pair potential and K-space and atom
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attributes which can be varied by this fix are discussed below. Many
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other fixes can also be used to time-vary simulation parameters,
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e.g. the "fix deform" command will change the simulation box
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size/shape and the "fix move" command will change atom positions and
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velocities in a prescribed manner.
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</P>
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<P>If <I>N</I> is specified as 0, the specified attributes are only changed
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once, before the simulation begins. This is all that is needed if the
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associated variables are not time-dependent. If <I>N</I> > 0, then changes
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are made every <I>N</I> steps during the simulation, presumably with a
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variable that is time-dependent.
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</P>
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<P>Depending on the value of the <I>reset</I> keyword, attributes changed by
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this fix will or will not be reset back to their original values at
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the end of a simulation. Even if <I>reset</I> is specified as <I>yes</I>, a
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restart file written during a simulation will contain the modified
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settings.
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</P>
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2010-10-23 06:22:51 +08:00
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<P>IMPORTANT NOTE: Currently, only the <I>pair</I> and <I>kspace</I> params
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are resettable. <I>Atom</I> attributes are not. This will be
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added at some point.
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</P>
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2010-10-23 05:24:19 +08:00
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<P>If the <I>scale</I> keyword is set to <I>no</I>, then the value the parameter is
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set to will be whatever the variable generates. If the <I>scale</I>
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keyword is set to <I>yes</I>, then the value of the altered parameter will
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be the initial value of that parameter multiplied by whatever the
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variable generates. I.e. the variable is now a "scale factor" applied
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in (presumably) a time-varying fashion to the parameter. Internally,
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the parameters themselves are actually altered; make sure you use the
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<I>reset yes</I> option if you want the parameters to be restored to their
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initial values after the run.
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2010-07-21 03:26:18 +08:00
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</P>
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2010-10-23 05:24:19 +08:00
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<HR>
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2010-06-22 22:52:12 +08:00
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<P>The <I>pair</I> keyword enables various parameters of potentials defined by
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the <A HREF = "pair_style.html">pair_style</A> command to be changed, if the pair
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2010-10-23 05:24:19 +08:00
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style supports it. Note that the <A HREF = "pair_style.html">pair_style</A> and
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<A HREF = "pair_coeff.html">pair_coeff</A> commands must be used in the usual manner
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to specify these parameters initially; the fix adapt command simply
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overrides the parameters.
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</P>
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<P>The <I>pstyle</I> argument is the name of the pair style. If <A HREF = "pair_hybrid.html">pair_style
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hybrid or hybrid/overlay</A> is used, <I>pstyle</I> should be
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a sub-style name. For example, <I>pstyle</I> could be specified as "soft"
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or "lubricate". The <I>pparam</I> argument is the name of the parameter to
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change. This is the current list of pair styles and parameters that
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can be varied by this fix. See the doc pages for individual pair
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styles and their energy formulas for the meaning of these parameters:
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2010-06-22 22:52:12 +08:00
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</P>
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<DIV ALIGN=center><TABLE BORDER=1 >
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2011-08-07 04:48:42 +08:00
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<TR><TD ><A HREF = "pair_born.html">born</A></TD><TD > a,b,c</TD><TD > type pairs</TD></TR>
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<TR><TD ><A HREF = "pair_buck.html">buck</A></TD><TD > a,c</TD><TD > type pairs</TD></TR>
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<TR><TD ><A HREF = "pair_coul.html">coul/cut</A></TD><TD > scale</TD><TD > type pairs</TD></TR>
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<TR><TD ><A HREF = "pair_coul.html">coul/debye</A></TD><TD > scale</TD><TD > type pairs</TD></TR>
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<TR><TD ><A HREF = "pair_coul.html">coul/long</A></TD><TD > scale</TD><TD > type pairs</TD></TR>
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<TR><TD ><A HREF = "pair_lj.html">lj/cut</A></TD><TD > epsilon</TD><TD > type pairs</TD></TR>
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<TR><TD ><A HREF = "pair_lj.html">lj/cut/opt</A></TD><TD > epsilon</TD><TD > type pairs</TD></TR>
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<TR><TD ><A HREF = "pair_lubricate.html">lubricate</A></TD><TD > mu</TD><TD > global</TD></TR>
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<TR><TD ><A HREF = "pair_gauss.html">gauss</A></TD><TD > a</TD><TD > type pairs</TD></TR>
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<TR><TD ><A HREF = "pair_soft.html">soft</A></TD><TD > a</TD><TD > type pairs
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2010-06-22 22:52:12 +08:00
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</TD></TR></TABLE></DIV>
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2010-10-23 06:01:31 +08:00
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<P>IMPORTANT NOTE: It is easy to add new potentials and their parameters
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to this list. All it typically takes is adding an extract() method to
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the pair_*.cpp file associated with the potential.
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</P>
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2010-06-22 22:52:12 +08:00
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<P>Some parameters are global settings for the pair style, e.g. the
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viscosity setting "mu" for <A HREF = "pair_lubricate.html">pair_style lubricate</A>.
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2010-10-23 05:24:19 +08:00
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Other parameters apply to atom type pairs within the pair style,
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e.g. the prefactor "a" for <A HREF = "pair_soft.html">pair_style soft</A>.
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</P>
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<P>Note that for many of the potentials, the parameter that can be varied
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is effectively a prefactor on the entire energy expression for the
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potential, e.g. the lj/cut epsilon. The parameters listed as "scale"
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are exactly that, since the energy expression for the
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<A HREF = "pair_coul.html">coul/cut</A> potential (for example) has no labeled
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prefactor in its formula. To apply an effective prefactor to some
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potentials, multiple parameters need to be altered. For example, the
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<A HREF = "pair_buck.html">Buckingham potential</A> needs both the A and C terms
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altered together. To scale the Buckingham potential, you should thus
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list the pair style twice, once for A and once for C.
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</P>
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<P>If a type pair parameter is specified, the <I>I</I> and <I>J</I> settings should
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be specified to indicate which type pairs to apply it to. If a global
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parameter is specified, the <I>I</I> and <I>J</I> settings still need to be
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specified, but are ignored.
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2010-06-22 22:52:12 +08:00
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</P>
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<P>Similar to the <A HREF = "pair_coeff.html">pair_coeff command</A>, I and J can be
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specified in one of two ways. Explicit numeric values can be used for
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each, as in the 1st example above. I <= J is required. LAMMPS sets
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the coefficients for the symmetric J,I interaction to the same values.
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</P>
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<P>A wild-card asterisk can be used in place of or in conjunction with
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the I,J arguments to set the coefficients for multiple pairs of atom
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types. This takes the form "*" or "*n" or "n*" or "m*n". If N = the
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number of atom types, then an asterisk with no numeric values means
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all types from 1 to N. A leading asterisk means all types from 1 to n
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(inclusive). A trailing asterisk means all types from n to N
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(inclusive). A middle asterisk means all types from m to n
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(inclusive). Note that only type pairs with I <= J are considered; if
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asterisks imply type pairs where J < I, they are ignored.
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</P>
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2010-10-23 05:24:19 +08:00
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<P>IMPROTANT NOTE: If <A HREF = "pair_hybrid.html">pair_style hybrid or
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hybrid/overlay</A> is being used, then the <I>pstyle</I> will
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be a sub-style name. You must specify I,J arguments that correspond
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to type pair values defined (via the <A HREF = "doc/pair_coeff.html">pair_coeff</A>
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command) for that sub-style.
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2010-06-22 22:52:12 +08:00
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</P>
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2010-08-13 07:10:38 +08:00
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<P>The <I>v_name</I> argument for keyword <I>pair</I> is the name of an
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<A HREF = "variable.html">equal-style variable</A> which will be evaluated each time
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this fix is invoked to set the parameter to a new value. It should be
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specified as v_name, where name is the variable name. Equal-style
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variables can specify formulas with various mathematical functions,
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and include <A HREF = "thermo_style.html">thermo_style</A> command keywords for the
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simulation box parameters and timestep and elapsed time. Thus it is
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easy to specify parameters that change as a function of time or span
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2010-06-22 22:52:12 +08:00
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consecutive runs in a continuous fashion. For the latter, see the
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<I>start</I> and <I>stop</I> keywords of the <A HREF = "run.html">run</A> command and the
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<I>elaplong</I> keyword of <A HREF = "thermo_style.html">thermo_style custom</A> for
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details.
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</P>
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<P>For example, these commands would change the prefactor coefficient of
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the <A HREF = "pair_soft.html">pair_style soft</A> potential from 10.0 to 30.0 in a
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2010-08-05 05:36:27 +08:00
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linear fashion over the course of a simulation:
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2010-06-22 22:52:12 +08:00
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</P>
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2010-08-05 05:36:27 +08:00
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<PRE>variable prefactor equal ramp(10,30)
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2010-08-13 07:10:38 +08:00
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fix 1 all adapt 1 pair soft a * * v_prefactor
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2010-06-22 22:52:12 +08:00
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</PRE>
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2010-10-23 05:24:19 +08:00
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<HR>
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<P>The <I>kspace</I> keyword used the specified variable as a scale factor on
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the energy, forces, virial calculated by whatever K-Space solver is
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defined by the <A HREF = "kspace_style.html">kspace_style</A> command. If the
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variable has a value of 1.0, then the solver is unaltered.
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</P>
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<P>The <I>kspace</I> keyword works this way whether the <I>scale</I> keyword
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is set to <I>no</I> or <I>yes</I>.
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</P>
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<HR>
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2010-06-22 22:52:12 +08:00
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<P>The <I>atom</I> keyword enables various atom properties to be changed. The
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<I>aparam</I> argument is the name of the parameter to change. This is the
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current list of atom parameters that can be varied by this fix:
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</P>
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<UL><LI>diameter = diameter of particle
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</UL>
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2010-08-13 07:10:38 +08:00
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<P>The <I>v_name</I> argument of the <I>atom</I> keyword is the name of an
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<A HREF = "variable.html">equal-style variable</A> which will be evaluated each time
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this fix is invoked to set the parameter to a new value. It should be
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specified as v_name, where name is the variable name. See the
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discussion above describing the formulas associated with equal-style
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variables. The new value is assigned to the corresponding attribute
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for all atoms in the fix group.
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2010-06-22 22:52:12 +08:00
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</P>
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2010-09-11 01:12:21 +08:00
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<P>If the atom parameter is <I>diameter</I> and per-atom density and per-atom
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mass are defined for particles (e.g. <A HREF = "atom_style.html">atom_style
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granular</A>), then the mass of each particle is also
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changed when the diameter changes (density is assumed to stay
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constant).
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</P>
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2010-06-22 22:52:12 +08:00
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<P>For example, these commands would shrink the diameter of all granular
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particles in the "center" group from 1.0 to 0.1 in a linear fashion
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over the course of a 1000-step simulation:
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</P>
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2010-08-13 07:10:38 +08:00
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<PRE>variable size equal ramp(1.0,0.1)
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fix 1 center adapt 10 atom diameter v_size
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2010-06-22 22:52:12 +08:00
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</PRE>
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<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
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</P>
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<P>No information about this fix is written to <A HREF = "restart.html">binary restart
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files</A>. None of the <A HREF = "fix_modify.html">fix_modify</A> options
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are relevant to this fix. No global or per-atom quantities are stored
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by this fix for access by various <A HREF = "Section_howto.html#4_15">output
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commands</A>. No parameter of this fix can be
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used with the <I>start/stop</I> keywords of the <A HREF = "run.html">run</A> command.
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This fix is not invoked during <A HREF = "minimize.html">energy minimization</A>.
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</P>
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<P><B>Restrictions:</B> none
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</P>
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2010-10-23 05:24:19 +08:00
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "compute_ti.html">compute ti</A>
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</P>
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<P><B>Default:</B>
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2010-06-22 22:52:12 +08:00
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</P>
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2010-10-23 05:24:19 +08:00
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<P>The option defaults are scale = no, reset = no.
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2010-06-22 22:52:12 +08:00
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</P>
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</HTML>
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