diff --git a/doc/src/compute_hma.txt b/doc/src/compute_hma.txt index c203c281ed..58934be054 100644 --- a/doc/src/compute_hma.txt +++ b/doc/src/compute_hma.txt @@ -37,8 +37,24 @@ energy, pressure or heat capacity), using the harmonically-mapped averaging (HMA) method. This command yields much higher precision than the equivalent compute commands ("compute pe"_compute_pe.html, "compute pressure"_compute_pressure.html, etc.) -commands during a canonical simulation of an atomic crystal. +commands during a canonical simulation of an atomic crystal. Specifically, +near melting HMA can yield averages of a given precision an order of magnitude +faster than conventional methods, and this only improves as the temperatures is +lowered. This is particularly important for evaluating the free energy by +thermodynamic integration, where the low-temperature contributions are the +greatest source of statistical uncertainty. Moreover, HMA has other +advantages, including smaller potential-truncation effects, finite-size +effects, smaller timestep inaccuracy, faster equilibration and shorter +decorrelation time. +HMA should not be used if atoms are expected to diffuse. It is also +restricted to simulations in the NVT ensemble. + +Computation of the heat capacity with this compute is presently restricted to +the "lj_smooth_linear"_lj_smooth_linear.html pair style. Use with other pair +styles requires an additional method (single2nd) to be implemented in the +corresponding Pair class. Computation of the energy and pressure does not +have this restriction. In this method, the analytically known harmonic behavior of a crystal is removed from the traditional ensemble averages, which leads to an accurate and precise measurement of the anharmonic contributions without contamination @@ -119,7 +135,9 @@ NOTE: Compute hma should be used when the atoms of the solid do not diffuse. Dif NOTE: The "fix_modify energy yes"_fix_modify.html command must also be specified if a fix is to contribute potential energy to this command. -:line +An example input script that uses this compute is included in +examples/USER/hma/ along with corresponding LAMMPS output showing that the HMA +properties fluctuate less than the corresponding conventional properties. [Output info:]