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@ -781,11 +781,11 @@ profile consistent with the applied shear strain rate.
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<A NAME = "4_14"></A><H4>4.14 Extended spherical and aspherical particles
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</H4>
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<P>Typical MD models treat atoms or particles as point masses.
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Sometimes, however, it is desirable to have a model where the
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particles are extended spherioids or extended aspherical paticles such
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as an ellipsoid. The difference is that such particles have a moment
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of inertia, rotational energy, and angular momentum. Rotation is
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induced by torque from interactions with other particles.
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Sometimes, however, it is desirable to have a model with finite-size
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particles such as spherioids or aspherical ellipsoids. The difference
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is that such particles have a moment of inertia, rotational energy,
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and angular momentum. Rotation is induced by torque from interactions
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with other particles.
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</P>
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<P>LAMMPS has several options for running simulations with these kinds of
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particles. The following aspects are discussed in turn:
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@ -798,14 +798,14 @@ particles. The following aspects are discussed in turn:
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</UL>
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<H5>Atom styles
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</H5>
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<P>There are 3 <A HREF = "atom_style.html">atom styles</A> that define extended
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particles: granular, dipole, ellipsoid.
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<P>There are 3 <A HREF = "atom_style.html">atom styles</A> that allow for definition of
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finite-size particles: granular, dipole, ellipsoid.
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</P>
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<P>Granular particles are extended spheriods and each particle can have a
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unique diameter and mass (or density). These particles store
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an angular velocity (omega) and can be acted upon by torque.
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<P>Granular particles are spheriods and each particle can have a unique
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diameter and mass (or density). These particles store an angular
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velocity (omega) and can be acted upon by torque.
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</P>
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<P>Dipole particles are extended spheriods with a point dipole and each
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<P>Dipolar particles are typically spheriods with a point dipole and each
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particle type has a diamater and mass, set by the <A HREF = "shape.html">shape</A>
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and <A HREF = "mass.html">mass</A> commands. These particles store an angular
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velocity (omega) and can be acted upon by torque. They also store an
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@ -817,31 +817,36 @@ to initialize the orientation of dipole moments.
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ellipsoidal shape and mass, defined by the <A HREF = "shape.html">shape</A> and
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<A HREF = "mass.html">mass</A> commands. These particles store an angular momentum
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and their orientation (quaternion), and can be acted upon by torque.
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They do not store an angular velocity (omega) which can be in a
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different direction than angular momentum. The <A HREF = "set.html">set</A> command
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can be used to initialize the orientation of ellipsoidal particles and
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has a brief explanation of quaternions.
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They do not store an angular velocity (omega), which can be in a
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different direction than angular momentum, rather they compute it as
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needed. Ellipsoidal particles can also store a dipole moment if an
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<A HREF = "atom_style.html">atom_style hybrid ellipsoid dipole</A> is used. The
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<A HREF = "set.html">set</A> command can be used to initialize the orientation of
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ellipsoidal particles and has a brief explanation of quaternions.
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</P>
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<P>Note that if one of these atom styles is used (or multiple styles via
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the <A HREF = "atom_style.html">atom_style hybrid</A> command), not all particles in
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the system are required to be extended or aspherical. For example, if
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the 3 shape parameters are set to the same value, the particle will be
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a spheroid rather than an ellipsoid. If the dipole moment is set to
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zero, the particle will not have a point dipole associated with it.
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The pair styles used to compute pairwise interactions will typically
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compute the correct interaction in these simplified (cheaper) cases.
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<A HREF = "pair_hybrid.html">Pair_style hybrid</A> can be used to insure the correct
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the system are required to be finite-size or aspherical. For example,
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if the 3 shape parameters are set to the same value, the particle will
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be a spheroid rather than an ellipsoid. If the 3 shape parameters are
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all set to 0.0 or if the diameter is set to 0.0, it will be a point
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particle. If the dipole moment is set to zero, the particle will not
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have a point dipole associated with it. The pair styles used to
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compute pairwise interactions will typically compute the correct
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interaction in these simplified (cheaper) cases. <A HREF = "pair_hybrid.html">Pair_style
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hybrid</A> can be used to insure the correct
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interactions are computed for the appropriate style of interactions.
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Likewise, using groups to partition particles (ellipsoid versus
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spheroid versus point particles) will allow you to use the appropriate
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time integrators and temperature computations for each class of
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particles. See the doc pages for various commands for details.
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</P>
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<P>Also note that for <A HREF = "dimension.html">2d simulations</A>, extended spheroids
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and ellipsoids are still treated as 3d particles, rather than as disks
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or ellipses. This means they still have a moment of inertia for a 3d
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extended object. When their temperature is coomputed, the correct
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degrees of freedom are used for rotation in a 2d versus 3d system.
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<P>Also note that for <A HREF = "dimension.html">2d simulations</A>, finite-size
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spheroids and ellipsoids are still treated as 3d particles, rather
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than as disks or ellipses. This means they have the same moment of
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inertia for a 3d extended object. When their temperature is
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coomputed, the correct degrees of freedom are used for rotation in a
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2d versus 3d system.
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</P>
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<H5>Pair potentials
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</H5>
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@ -927,8 +932,8 @@ particles as a rigid body, computes its inertia tensor, sums the total
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force and torque on the rigid body each timestep due to forces on its
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constituent particles, and integrates the motion of the rigid body.
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</P>
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<P>(NOTE: 6/08 the feature described in the following paragraph has
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not yet been released. It will be soon.)
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<P>(NOTE: the feature described in the following paragraph has not yet
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been released. It will be soon.)
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</P>
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<P>If any of the constituent particles of a rigid body are extended
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particles (spheroids or ellipsoids), then their contribution to the
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|
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@ -774,11 +774,11 @@ An alternative method for calculating viscosities is provided via the
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4.14 Extended spherical and aspherical particles :link(4_14),h4
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Typical MD models treat atoms or particles as point masses.
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Sometimes, however, it is desirable to have a model where the
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particles are extended spherioids or extended aspherical paticles such
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as an ellipsoid. The difference is that such particles have a moment
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of inertia, rotational energy, and angular momentum. Rotation is
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induced by torque from interactions with other particles.
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Sometimes, however, it is desirable to have a model with finite-size
|
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particles such as spherioids or aspherical ellipsoids. The difference
|
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is that such particles have a moment of inertia, rotational energy,
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and angular momentum. Rotation is induced by torque from interactions
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with other particles.
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LAMMPS has several options for running simulations with these kinds of
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particles. The following aspects are discussed in turn:
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@ -791,14 +791,14 @@ rigid bodies composed of extended particles :ul
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Atom styles :h5
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There are 3 "atom styles"_atom_style.html that define extended
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particles: granular, dipole, ellipsoid.
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There are 3 "atom styles"_atom_style.html that allow for definition of
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finite-size particles: granular, dipole, ellipsoid.
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Granular particles are extended spheriods and each particle can have a
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unique diameter and mass (or density). These particles store
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an angular velocity (omega) and can be acted upon by torque.
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Granular particles are spheriods and each particle can have a unique
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diameter and mass (or density). These particles store an angular
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velocity (omega) and can be acted upon by torque.
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Dipole particles are extended spheriods with a point dipole and each
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Dipolar particles are typically spheriods with a point dipole and each
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particle type has a diamater and mass, set by the "shape"_shape.html
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and "mass"_mass.html commands. These particles store an angular
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velocity (omega) and can be acted upon by torque. They also store an
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@ -810,31 +810,36 @@ Ellipsoid particles are aspherical. Each particle type has an
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ellipsoidal shape and mass, defined by the "shape"_shape.html and
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"mass"_mass.html commands. These particles store an angular momentum
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and their orientation (quaternion), and can be acted upon by torque.
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They do not store an angular velocity (omega) which can be in a
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different direction than angular momentum. The "set"_set.html command
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can be used to initialize the orientation of ellipsoidal particles and
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has a brief explanation of quaternions.
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They do not store an angular velocity (omega), which can be in a
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different direction than angular momentum, rather they compute it as
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needed. Ellipsoidal particles can also store a dipole moment if an
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"atom_style hybrid ellipsoid dipole"_atom_style.html is used. The
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"set"_set.html command can be used to initialize the orientation of
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ellipsoidal particles and has a brief explanation of quaternions.
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Note that if one of these atom styles is used (or multiple styles via
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the "atom_style hybrid"_atom_style.html command), not all particles in
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the system are required to be extended or aspherical. For example, if
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the 3 shape parameters are set to the same value, the particle will be
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a spheroid rather than an ellipsoid. If the dipole moment is set to
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zero, the particle will not have a point dipole associated with it.
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The pair styles used to compute pairwise interactions will typically
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compute the correct interaction in these simplified (cheaper) cases.
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"Pair_style hybrid"_pair_hybrid.html can be used to insure the correct
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the system are required to be finite-size or aspherical. For example,
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if the 3 shape parameters are set to the same value, the particle will
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be a spheroid rather than an ellipsoid. If the 3 shape parameters are
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all set to 0.0 or if the diameter is set to 0.0, it will be a point
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particle. If the dipole moment is set to zero, the particle will not
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have a point dipole associated with it. The pair styles used to
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compute pairwise interactions will typically compute the correct
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interaction in these simplified (cheaper) cases. "Pair_style
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hybrid"_pair_hybrid.html can be used to insure the correct
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interactions are computed for the appropriate style of interactions.
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Likewise, using groups to partition particles (ellipsoid versus
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spheroid versus point particles) will allow you to use the appropriate
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time integrators and temperature computations for each class of
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particles. See the doc pages for various commands for details.
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Also note that for "2d simulations"_dimension.html, extended spheroids
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and ellipsoids are still treated as 3d particles, rather than as disks
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or ellipses. This means they still have a moment of inertia for a 3d
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extended object. When their temperature is coomputed, the correct
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degrees of freedom are used for rotation in a 2d versus 3d system.
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Also note that for "2d simulations"_dimension.html, finite-size
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spheroids and ellipsoids are still treated as 3d particles, rather
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than as disks or ellipses. This means they have the same moment of
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inertia for a 3d extended object. When their temperature is
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coomputed, the correct degrees of freedom are used for rotation in a
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2d versus 3d system.
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Pair potentials :h5
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@ -920,8 +925,8 @@ particles as a rigid body, computes its inertia tensor, sums the total
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force and torque on the rigid body each timestep due to forces on its
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constituent particles, and integrates the motion of the rigid body.
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(NOTE: 6/08 the feature described in the following paragraph has
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not yet been released. It will be soon.)
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(NOTE: the feature described in the following paragraph has not yet
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been released. It will be soon.)
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If any of the constituent particles of a rigid body are extended
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particles (spheroids or ellipsoids), then their contribution to the
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|
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