A 6-component symmetric pressure tensor is also calculated by this +compute whose components can be output by the thermo_style custom command or accessed by other -compute and fix commands. The equation for -the components of the tensor is the same as in above formula, except -that the first term uses the components of the kinetic energy tensor -(vx * vy instead of v^2 for temperature) and the second term uses Rx * -Fy for the Wxy component of the virial tensor, etc. +compute and fix commands. The 6 values are +1 = Pxx, 2 = Pyy, 3 = Pzz, 4 = Pxy, 5 = Pxz, 6 = Pyz. The equation +for the I,J components (where I and J = x,y,z) is similar to the above +formula, except that the first term uses components of the kinetic +energy tensor and the second term uses components of the virial +tensor:
-If no extra keywords are listed, the entire equation above is -calculated which includes a temperature term (or kinetic energy -tensor) and the virial as the sum of pair, bond, angle, dihedral, -improper, kspace (long-range), and fix contributions. If any extra -keywords are listed, then only those components are summed to compute -ke and/or the virial. +
+If no extra keywords are listed, the entire equations above are +calculated which include a temperature (or kinetic energy) term and +the virial as the sum of pair, bond, angle, dihedral, improper, kspace +(long-range), and fix contributions to the force on each atom. If any +extra keywords are listed, then only those components are summed to +compute temperature or ke and/or the virial.
The temperature and kinetic energy tensor is not calculated by this compute, but rather by the temperature compute specified with the @@ -70,9 +73,10 @@ all atoms for consistency with the virial term, but any compute style that calculates temperature can be used, e.g. one that excludes frozen atoms or other degrees of freedom.
-Note that the N is the above formula is really degrees-of-freedom -where the DOF is specified by the temperature compute. See the -various compute temperature styles for details. +
Note that the N in the first formula above is really +degrees-of-freedom divided by 3, where the DOF is calcluated by the +temperature compute. See the various compute +temperature styles for details.
A compute of this style with the ID of "thermo_press" is created when LAMMPS starts up, as if this command were in the input script: diff --git a/doc/compute_pressure.txt b/doc/compute_pressure.txt index 4b9ae520d2..89f62a6651 100644 --- a/doc/compute_pressure.txt +++ b/doc/compute_pressure.txt @@ -44,21 +44,24 @@ and long-range interactions. "Fixes"_fix.html that impose constraints (e.g. the "fix shake"_fix_shake.html command) also contribute to the virial term. -A 6-component pressure tensor is also calculated by this compute whose -components can be output by the "thermo_style +A 6-component symmetric pressure tensor is also calculated by this +compute whose components can be output by the "thermo_style custom"_thermo_style.html command or accessed by other -"compute"_compute.html and "fix"_fix.html commands. The equation for -the components of the tensor is the same as in above formula, except -that the first term uses the components of the kinetic energy tensor -(vx * vy instead of v^2 for temperature) and the second term uses Rx * -Fy for the Wxy component of the virial tensor, etc. +"compute"_compute.html and "fix"_fix.html commands. The 6 values are +1 = Pxx, 2 = Pyy, 3 = Pzz, 4 = Pxy, 5 = Pxz, 6 = Pyz. The equation +for the I,J components (where I and J = x,y,z) is similar to the above +formula, except that the first term uses components of the kinetic +energy tensor and the second term uses components of the virial +tensor: -If no extra keywords are listed, the entire equation above is -calculated which includes a temperature term (or kinetic energy -tensor) and the virial as the sum of pair, bond, angle, dihedral, -improper, kspace (long-range), and fix contributions. If any extra -keywords are listed, then only those components are summed to compute -ke and/or the virial. +:c,image(Eqs/pressure_tensor.jpg) + +If no extra keywords are listed, the entire equations above are +calculated which include a temperature (or kinetic energy) term and +the virial as the sum of pair, bond, angle, dihedral, improper, kspace +(long-range), and fix contributions to the force on each atom. If any +extra keywords are listed, then only those components are summed to +compute temperature or ke and/or the virial. The temperature and kinetic energy tensor is not calculated by this compute, but rather by the temperature compute specified with the @@ -67,9 +70,10 @@ all atoms for consistency with the virial term, but any compute style that calculates temperature can be used, e.g. one that excludes frozen atoms or other degrees of freedom. -Note that the N is the above formula is really degrees-of-freedom -where the DOF is specified by the temperature compute. See the -various "compute temperature"_compute.html styles for details. +Note that the N in the first formula above is really +degrees-of-freedom divided by 3, where the DOF is calcluated by the +temperature compute. See the various "compute +temperature"_compute.html styles for details. A compute of this style with the ID of "thermo_press" is created when LAMMPS starts up, as if this command were in the input script: