Loading doc/fix_dt_reset.html +22 −20 Original line number Diff line number Diff line Loading @@ -18,8 +18,8 @@ <UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command <LI>dt/reset = style name of this fix command <LI>N = recompute dt every N timesteps <LI>Tmin = minimum dt allowed (can be INF) (time units) <LI>Tmax = maximum dt allowed (can be INF) (time units) <LI>Tmin = minimum dt allowed (can be NULL) (time units) <LI>Tmax = maximum dt allowed (can be NULL) (time units) <LI>Xmax = maximum distance for an atom to move in one timestep (distance units) <LI>zero or more keyword/value pairs may be appended <LI>keyword = <I>units</I> Loading @@ -35,27 +35,29 @@ fix 5 all dt/reset 10 0.01 2.0 0.2 units box </PRE> <P><B>Description:</B> </P> <P>Reset the timestep size every N steps during a run, based on current atom velocities and forces. This can be useful when starting from a configuration with overlapping atoms, where forces will be large. Or it can be useful when running an impact simulation where one or more high-energy atoms collide with a solid, causing a damage cascade. <P>Reset the timestep size every N steps during a run, so that no atom moves further than Xmax, based on current atom velocities and forces. This can be useful when starting from a configuration with overlapping atoms, where forces will be large. Or it can be useful when running an impact simulation where one or more high-energy atoms collide with a solid, causing a damage cascade. </P> <P>This fix overrides the timestep size setting made by the <A HREF = "timestep.html">timestep</A> command. The new timestep size <I>dt</I> is computed in the following way. </P> <UL><LI>compute Vmax of any atom in group <LI>compute Amax of any atom in group <LI>dt1 = Xmax/Vmax <LI>dt2 = sqrt(2 Xmax/Amax) <LI>new dt = MIN(dt1,dt2) <LI>if dt < Tmin, dt = Tmin <LI>if dt > Tmax, dt = Tmax </UL> <P>Vmax is the maximum velocity; Amax is the maximum acceleration = force/mass. Note that Tmin or Tmax can be specified as INF, in which case one or both of the last 2 checks will not be performed. computed in the following manner. </P> <P>For each atom, the timestep is computed that would cause it to displace <I>Xmax</I> on the next integration step, as a function of its current velocity and force. Since performing this calculation exactly would require the solution to a quartic equation, a cheaper estimate is generated. The estimate is conservative in that the atom's displacement is guaranteed not to exceed <I>Xmax</I>, though it may be smaller. </P> <P>Given this putative timestep for each atom, the minimum timestep value across all atoms is computed. Then the <I>Tmin</I> and <I>Tmax</I> bounds are applied, if specified. If one (or both) is specified as NULL, it is not applied. </P> <P>When the <A HREF = "run_style.html">run style</A> is <I>respa</I>, this fix resets the outer loop (largest) timestep, which is the same timestep that the Loading doc/fix_dt_reset.txt +22 −20 Original line number Diff line number Diff line Loading @@ -15,8 +15,8 @@ fix ID group-ID dt/reset N Tmin Tmax Xmax keyword values ... :pre ID, group-ID are documented in "fix"_fix.html command dt/reset = style name of this fix command N = recompute dt every N timesteps Tmin = minimum dt allowed (can be INF) (time units) Tmax = maximum dt allowed (can be INF) (time units) Tmin = minimum dt allowed (can be NULL) (time units) Tmax = maximum dt allowed (can be NULL) (time units) Xmax = maximum distance for an atom to move in one timestep (distance units) zero or more keyword/value pairs may be appended keyword = {units} :ul Loading @@ -31,27 +31,29 @@ fix 5 all dt/reset 10 0.01 2.0 0.2 units box :pre [Description:] Reset the timestep size every N steps during a run, based on current atom velocities and forces. This can be useful when starting from a configuration with overlapping atoms, where forces will be large. Or it can be useful when running an impact simulation where one or more high-energy atoms collide with a solid, causing a damage cascade. Reset the timestep size every N steps during a run, so that no atom moves further than Xmax, based on current atom velocities and forces. This can be useful when starting from a configuration with overlapping atoms, where forces will be large. Or it can be useful when running an impact simulation where one or more high-energy atoms collide with a solid, causing a damage cascade. This fix overrides the timestep size setting made by the "timestep"_timestep.html command. The new timestep size {dt} is computed in the following way. compute Vmax of any atom in group compute Amax of any atom in group dt1 = Xmax/Vmax dt2 = sqrt(2 Xmax/Amax) new dt = MIN(dt1,dt2) if dt < Tmin, dt = Tmin if dt > Tmax, dt = Tmax :ul Vmax is the maximum velocity; Amax is the maximum acceleration = force/mass. Note that Tmin or Tmax can be specified as INF, in which case one or both of the last 2 checks will not be performed. computed in the following manner. For each atom, the timestep is computed that would cause it to displace {Xmax} on the next integration step, as a function of its current velocity and force. Since performing this calculation exactly would require the solution to a quartic equation, a cheaper estimate is generated. The estimate is conservative in that the atom's displacement is guaranteed not to exceed {Xmax}, though it may be smaller. Given this putative timestep for each atom, the minimum timestep value across all atoms is computed. Then the {Tmin} and {Tmax} bounds are applied, if specified. If one (or both) is specified as NULL, it is not applied. When the "run style"_run_style.html is {respa}, this fix resets the outer loop (largest) timestep, which is the same timestep that the Loading Loading
doc/fix_dt_reset.html +22 −20 Original line number Diff line number Diff line Loading @@ -18,8 +18,8 @@ <UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command <LI>dt/reset = style name of this fix command <LI>N = recompute dt every N timesteps <LI>Tmin = minimum dt allowed (can be INF) (time units) <LI>Tmax = maximum dt allowed (can be INF) (time units) <LI>Tmin = minimum dt allowed (can be NULL) (time units) <LI>Tmax = maximum dt allowed (can be NULL) (time units) <LI>Xmax = maximum distance for an atom to move in one timestep (distance units) <LI>zero or more keyword/value pairs may be appended <LI>keyword = <I>units</I> Loading @@ -35,27 +35,29 @@ fix 5 all dt/reset 10 0.01 2.0 0.2 units box </PRE> <P><B>Description:</B> </P> <P>Reset the timestep size every N steps during a run, based on current atom velocities and forces. This can be useful when starting from a configuration with overlapping atoms, where forces will be large. Or it can be useful when running an impact simulation where one or more high-energy atoms collide with a solid, causing a damage cascade. <P>Reset the timestep size every N steps during a run, so that no atom moves further than Xmax, based on current atom velocities and forces. This can be useful when starting from a configuration with overlapping atoms, where forces will be large. Or it can be useful when running an impact simulation where one or more high-energy atoms collide with a solid, causing a damage cascade. </P> <P>This fix overrides the timestep size setting made by the <A HREF = "timestep.html">timestep</A> command. The new timestep size <I>dt</I> is computed in the following way. </P> <UL><LI>compute Vmax of any atom in group <LI>compute Amax of any atom in group <LI>dt1 = Xmax/Vmax <LI>dt2 = sqrt(2 Xmax/Amax) <LI>new dt = MIN(dt1,dt2) <LI>if dt < Tmin, dt = Tmin <LI>if dt > Tmax, dt = Tmax </UL> <P>Vmax is the maximum velocity; Amax is the maximum acceleration = force/mass. Note that Tmin or Tmax can be specified as INF, in which case one or both of the last 2 checks will not be performed. computed in the following manner. </P> <P>For each atom, the timestep is computed that would cause it to displace <I>Xmax</I> on the next integration step, as a function of its current velocity and force. Since performing this calculation exactly would require the solution to a quartic equation, a cheaper estimate is generated. The estimate is conservative in that the atom's displacement is guaranteed not to exceed <I>Xmax</I>, though it may be smaller. </P> <P>Given this putative timestep for each atom, the minimum timestep value across all atoms is computed. Then the <I>Tmin</I> and <I>Tmax</I> bounds are applied, if specified. If one (or both) is specified as NULL, it is not applied. </P> <P>When the <A HREF = "run_style.html">run style</A> is <I>respa</I>, this fix resets the outer loop (largest) timestep, which is the same timestep that the Loading
doc/fix_dt_reset.txt +22 −20 Original line number Diff line number Diff line Loading @@ -15,8 +15,8 @@ fix ID group-ID dt/reset N Tmin Tmax Xmax keyword values ... :pre ID, group-ID are documented in "fix"_fix.html command dt/reset = style name of this fix command N = recompute dt every N timesteps Tmin = minimum dt allowed (can be INF) (time units) Tmax = maximum dt allowed (can be INF) (time units) Tmin = minimum dt allowed (can be NULL) (time units) Tmax = maximum dt allowed (can be NULL) (time units) Xmax = maximum distance for an atom to move in one timestep (distance units) zero or more keyword/value pairs may be appended keyword = {units} :ul Loading @@ -31,27 +31,29 @@ fix 5 all dt/reset 10 0.01 2.0 0.2 units box :pre [Description:] Reset the timestep size every N steps during a run, based on current atom velocities and forces. This can be useful when starting from a configuration with overlapping atoms, where forces will be large. Or it can be useful when running an impact simulation where one or more high-energy atoms collide with a solid, causing a damage cascade. Reset the timestep size every N steps during a run, so that no atom moves further than Xmax, based on current atom velocities and forces. This can be useful when starting from a configuration with overlapping atoms, where forces will be large. Or it can be useful when running an impact simulation where one or more high-energy atoms collide with a solid, causing a damage cascade. This fix overrides the timestep size setting made by the "timestep"_timestep.html command. The new timestep size {dt} is computed in the following way. compute Vmax of any atom in group compute Amax of any atom in group dt1 = Xmax/Vmax dt2 = sqrt(2 Xmax/Amax) new dt = MIN(dt1,dt2) if dt < Tmin, dt = Tmin if dt > Tmax, dt = Tmax :ul Vmax is the maximum velocity; Amax is the maximum acceleration = force/mass. Note that Tmin or Tmax can be specified as INF, in which case one or both of the last 2 checks will not be performed. computed in the following manner. For each atom, the timestep is computed that would cause it to displace {Xmax} on the next integration step, as a function of its current velocity and force. Since performing this calculation exactly would require the solution to a quartic equation, a cheaper estimate is generated. The estimate is conservative in that the atom's displacement is guaranteed not to exceed {Xmax}, though it may be smaller. Given this putative timestep for each atom, the minimum timestep value across all atoms is computed. Then the {Tmin} and {Tmax} bounds are applied, if specified. If one (or both) is specified as NULL, it is not applied. When the "run style"_run_style.html is {respa}, this fix resets the outer loop (largest) timestep, which is the same timestep that the Loading
