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git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@632 f3b2605a-c512-4ea7-a41b-209d697bcdaa

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2007-06-20 17:08:17 +00:00
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149
doc/fix_deform.html
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@ -25,7 +25,7 @@
<PRE>parameter = <I>x</I> or <I>y</I> or <I>z</I> or <I>xy</I> or <I>xz</I> or <I>yz</I>
<I>x</I>, <I>y</I>, <I>z</I> args = style value(s)
style = <I>final</I> or <I>delta</I> or <I>scale</I> or <I>vel</I> or <I>rate</I> or <I>volume</I>
style = <I>final</I> or <I>delta</I> or <I>scale</I> or <I>vel</I> or <I>erate</I> or <I>trate</I> or <I>volume</I>
<I>final</I> values = lo hi
lo hi = box boundaries at end of run (distance units)
<I>delta</I> values = dlo dhi
@ -35,11 +35,13 @@
<I>vel</I> value = V
V = change box length at this velocity (distance/time units),
effectively an engineering strain rate
<I>rate</I> value = R
<I>erate</I> value = R
R = engineering strain rate (1/time units)
<I>trate</I> value = R
R = true strain rate (1/time units)
<I>volume</I> value = none = adjust this dim to preserve volume of system
<I>xy</I>, <I>xz</I>, <I>yz</I> args = style value
style = <I>final</I> or <I>delta</I> or <I>vel</I> or <I>rate</I>
style = <I>final</I> or <I>delta</I> or <I>vel</I> or <I>erate</I> or <I>trate</I>
<I>final</I> value = tilt
tilt = tilt factor at end of run (distance units)
<I>delta</I> value = dtilt
@ -47,7 +49,10 @@
<I>vel</I> value = V
V = change tilt factor at this velocity (distance/time units),
effectively an engineering shear strain rate
<I>rate</I> value = R
<I>erate</I> value = R
R = engineering shear strain rate (1/time units)
</PRE>
<PRE> <I>trate</I> value = R
R = true shear strain rate (1/time units)
</PRE>
<LI>zero or more keyword/value pairs may be appended to the args
@ -67,8 +72,8 @@
<P><B>Examples:</B>
</P>
<PRE>fix 1 all deform x final 0.0 9.0 z final 0.0 5.0 units box
fix 1 all deform x rate 0.1 y volume z volume
fix 1 all deform xy rate 0.001 remap v
fix 1 all deform x trate 0.1 y volume z volume
fix 1 all deform xy erate 0.001 remap v
fix 1 all deform y delta 0.5 xz vel 1.0
</PRE>
<P><B>Description:</B>
@ -114,10 +119,11 @@ the ramping take place across multiple runs.
<P>For the <I>x</I>, <I>y</I>, and <I>z</I> parameters, this is the meaning of their
styles and values.
</P>
<P>The <I>final</I>, <I>delta</I>, <I>scale</I>, and <I>vel</I> styles all change the
specified dimension of the box via "constant displacement" which is
effectively a "constant engineering strain rate". This means the box
dimension changes linearly with time from its initial to final value.
<P>The <I>final</I>, <I>delta</I>, <I>scale</I>, <I>vel</I>, and <I>erate</I> styles all change
the specified dimension of the box via "constant displacement" which
is effectively a "constant engineering strain rate". This means the
box dimension changes linearly with time from its initial to final
value.
</P>
<P>For style <I>final</I>, the final lo and hi box boundaries of a dimension
are specified. The values can be in lattice or box distance units.
@ -133,36 +139,57 @@ is 10, and the factor is 1.1, then the final box length will be 11. A
factor less than 1.0 means compression.
</P>
<P>For style <I>vel</I>, a velocity at which the box length changes is
specified in units of distance/time. This is effectively an
"engineering strain rate", where rate = V/L0 and L0 is the initial box
specified in units of distance/time. This is effectively a "constant
engineering strain rate", where rate = V/L0 and L0 is the initial box
length. The distance can be in lattice or box distance units. See
the discussion of the units keyword below. For example, if the
initial box length is 100 Angstroms, and V is 10 Angstroms/psec,
then after 10 psec, the box length will have doubled. After 20 psec,
it will have tripled.
initial box length is 100 Angstroms, and V is 10 Angstroms/psec, then
after 10 psec, the box length will have doubled. After 20 psec, it
will have tripled.
</P>
<P>The <I>rate</I> style changes a dimension of the box at a "true constant
<P>The <I>erate</I> style changes a dimension of the the box at a "constant
engineering strain rate". The units of the specified strain rate are
1/time. See the <A HREF = "units.html">units</A> command for the time units
associated with different choices of simulation units,
e.g. picoseconds for "metal" units). Tensile strain is unitless and
is defined as delta/length0, where length0 is the original box length
and delta is the change relative to the original length. Thus if the
<I>erate</I> R is 0.1 and time units are picoseconds, this means the box
length will increase by 10% of its original length every picosecond.
I.e. strain after 1 psec = 0.1, strain after 2 psec = 0.2, etc.
R = -0.01 means the box length will shrink by 1% of its original
length every picosecond. Note that for an "engineering" rate the
change is based on the original box length, so running with R = 1 for
10 picoseconds expands the box length by a factor of 10, not 1024 as
it would with <I>trate</I>.
</P>
<P>The <I>trate</I> style changes a dimension of the box at a "constant true
strain rate". Note that this is not an "engineering strain rate", as
the other styles are. Rather, for a "true" rate, the rate of change
is constant, which means the box dimension changes non-linearly with
time from its initial to final value. The units of the specified
strain rate are 1/time. See the <A HREF = "units.html">units</A> command for the
time units associated with different choices of simulation units,
e.g. picoseconds for "metal" units). Thus if the <I>rate</I> R is 0.01 and
time units are picoseconds, this means the box length will increase by
1% every picosecond. R = 1 or 2 means the box length will double or
triple every picosecond. R = -0.1 means the box length will shrink by
10% every picosecond. Note that for a "true" rate the change is
continuous, so running with R = 1 for 10 picoseconds does not expand
the box length by a factor of 10, but by a factor of 1024 since it
doubles every picosecond.
e.g. picoseconds for "metal" units). Tensile strain is unitless and
is defined as delta/length0, where length0 is the original box length
and delta is the change relative to the original length. Thus if the
<I>trate</I> R is 0.1 and time units are picoseconds, this means the box
length will increase by 10% of its current length every picosecond.
I.e. strain after 1 psec = 0.1, strain after 2 psec = 0.21, etc.
R = 1 or 2 means the box length will double or triple every
picosecond. R = -0.01 means the box length will shrink by 1% of its
current length every picosecond. Note that for a "true" rate the
change is continuous and based on the current length, so running with
R = 1 for 10 picoseconds does not expand the box length by a factor of
10 as it would with <I>erate</I>, but by a factor of 1024 since it doubles
every picosecond.
</P>
<P>Note that to change the volume (or cross-sectional area) of the
simulation box at a constant rate, you can change multiple dimensions
via <I>rate</I>. E.g. to double the box volume every picosecond, you could
set "x rate M", "y rate M", "z rate M", with M = pow(2,1/3) - 1 =
1.26, since if each box dimension grows by 26%, the box volume
doubles.
via <I>erate</I> or <I>trate</I>. E.g. to double the box volume every
picosecond, you could set "x trate M", "y trate M", "z trate M", with
M = pow(2,1/3) - 1 = 1.26, since if each box dimension grows by 26%,
the box volume doubles.
</P>
<P>The <I>volume</I> style changes the specified dimension in such a way that
the box volume remains constant while other box dimensions are changed
@ -187,8 +214,8 @@ potentials whose Poisson ratio is not 0.5. An alternative is to use
<A HREF = "fix_npt.html">fix npt aniso</A> with zero applied pressure on those 2
dimensions, so that they respond to the tensile strain dynamically.
</P>
<P>For the <I>scale</I>, <I>vel</I>, <I>rate</I>, and <I>volume</I> styles, the box length is
expanded or compressed around its mid point.
<P>For the <I>scale</I>, <I>vel</I>, <I>erate</I>, <I>trate</I>, and <I>volume</I> styles, the box
length is expanded or compressed around its mid point.
</P>
<HR>
@ -196,6 +223,11 @@ expanded or compressed around its mid point.
styles and values. Note that changing the tilt factors of a triclinic
box does not change its volume.
</P>
<P>The <I>final</I>, <I>delta</I>, <I>vel</I>, and <I>erate</I> styles all change the shear
strain at a "constant engineering shear strain rate". This means the
tilt factor changes linearly with time from its initial to final
value.
</P>
<P>For style <I>final</I>, the final tilt factor is specified. The value
can be in lattice or box distance units. See the discussion of the
units keyword below.
@ -214,28 +246,53 @@ is 5 Angstroms, and the V is 10 Angstroms/psec, then after 1 psec, the
tilt factor will be 15 Angstroms. After 2 psec, it will be 25
Angstroms.
</P>
<P>The <I>rate</I> style changes a tilt factor at a "true constant shear
<P>The <I>erate</I> style changes a tilt factor at a "constant engineering
shear strain rate". The units of the specified shear strain rate are
1/time. See the <A HREF = "units.html">units</A> command for the time units
associated with different choices of simulation units,
e.g. picoseconds for "metal" units). Shear strain is unitless and is
defined as offset/length, where length is the box length perpendicular
to the shear direction (e.g. y box length for xy deformation) and
offset is the displacement distance in the shear direction (e.g. x
direction for xy deformation) from the unstrained orientation. Thus
if the <I>erate</I> R is 0.1 and time units are picoseconds, this means the
shear strain will increase by 0.1 every picosecond. I.e. if the xy
shear strain was initially 0.0, then strain after 1 psec = 0.1, strain
after 2 psec = 0.2, etc. Thus the tilt factor would be 0.0 at time 0,
0.1*ybox at 1 psec, 0.2*ybox at 2 psec, etc, where ybox is the
original y box length. R = 1 or 2 means the tilt factor will increase
by 1 or 2 every picosecond. R = -0.01 means a decrease in shear
strain by 0.01 every picosecond.
</P>
<P>The <I>trate</I> style changes a tilt factor at a "constant true shear
strain rate". Note that this is not an "engineering shear strain
rate", as the other styles are. Rather, for a "true" rate, the rate
of change is constant, which means the tilt factor changes
non-linearly with time from its initial to final value. The units of
shear strain rate are 1/time. See the <A HREF = "units.html">units</A> command for
the time units associated with different choices of simulation units,
e.g. picoseconds for "metal" units). Thus if the <I>rate</I> R is 0.01 and
time units are picoseconds, this means the tilt factor will increase
by 1% every picosecond. R = 1 or 2 means the tilt factor will double
or triple every picosecond. R = -0.1 means the tilt factor will
shrink by 10% every picosecond. Note that the change is continuous,
so running with R = 1 for 10 picoseconds does not change the tilt
factor by a factor of 10, but by a factor of 1024 since it doubles
every picosecond. Also note, that the initial tilt factor must be
non-zero to use the <I>rate</I> option.
the specified shear strain rate are 1/time. See the
<A HREF = "units.html">units</A> command for the time units associated with
different choices of simulation units, e.g. picoseconds for "metal"
units). Shear strain is unitless and is defined as offset/length,
where length is the box length perpendicular to the shear direction
(e.g. y box length for xy deformation) and offset is the displacement
distance in the shear direction (e.g. x direction for xy deformation)
from the unstrained orientation. Thus if the <I>trate</I> R is 0.1 and
time units are picoseconds, this means the shear strain or tilt factor
will increase by 10% every picosecond. I.e. if the xy shear strain
was initially 0.1, then strain after 1 psec = 0.11, strain after 2
psec = 0.121, etc. R = 1 or 2 means the tilt factor will double or
triple every picosecond. R = -0.01 means the tilt factor will shrink
by 1% every picosecond. Note that the change is continuous, so
running with R = 1 for 10 picoseconds does not change the tilt factor
by a factor of 10, but by a factor of 1024 since it doubles every
picosecond. Also note that the initial tilt factor must be non-zero
to use the <I>trate</I> option.
</P>
<P>Note that shear strain is defined as the tilt factor divided by the
perpendicular box length. The <I>rate</I> style controls the tilt factor,
but assumes the perpendicular box length remains constant. If this is
not the case (e.g. it changes due to another fix deform parameter),
then this effect on the shear strain is ignored.
perpendicular box length. The <I>erate</I> and <I>trate</I> styles control the
tilt factor, but assume the perpendicular box length remains constant.
If this is not the case (e.g. it changes due to another fix deform
parameter), then this effect on the shear strain is ignored.
</P>
<P>All of these styles change the xy, xz, yz tilt factors during a
simulation. In LAMMPS, tilt factors (xy,xz,yz) for triclinic boxes