diff --git a/doc/src/fix_pimd.rst b/doc/src/fix_pimd.rst
index 1767acb134..fda002484a 100644
--- a/doc/src/fix_pimd.rst
+++ b/doc/src/fix_pimd.rst
@@ -269,13 +269,25 @@ related tasks for each of the partitions, e.g.
    read_restart system_${ibead}.restart2
 
 .. note::
-   Fix *pimd/langevin* dumps the Catersian coordinates, but dumps the velocities and
-   forces in the normal mode representation. If the Catersian velocities and forces are
+   Fix *pimd/langevin* dumps the Cartesian coordinates, but dumps the velocities and
+   forces in the normal mode representation. If the Cartesian velocities and forces are
    needed, it is easy to perform the transformation when doing post-processing.
 
    It is recommended to dump the image flags (*ix iy iz*) for fix *pimd/langevin*. It
    will be useful if you want to calculate some estimators during post-processing.
 
+Major differences of *fix pimd/nvt* and *fix pimd/langevin* are:
+
+   #. *Fix pimd/nvt* includes Cartesian pimd, normal mode pimd, and centroid md. *Fix pimd/langevin* only intends to support normal mode pimd, as it is commonly enough for thermodynamic sampling.
+   #. *Fix pimd/nvt* uses Nose-Hoover chain thermostat. *Fix pimd/langevin* uses Langevin thermostat.
+   #. *Fix pimd/langevin* provides barostat, so the npt ensemble can be sampled. *Fix pimd/nvt* only support nvt ensemble.
+   #. *Fix pimd/langevin* provides several quantum estimators in output.
+   #. *Fix pimd/langevin* allows multiple processes for each bead. For *fix pimd/nvt*, there is a large chance that multi-process tasks for each bead may fail.
+   #. The dump of *fix pimd/nvt* are all Cartesian. *Fix pimd/langevin* dumps normal-mode velocities and forces, and Cartesian coordinates.
+
+Initially, the inter-replica communication and normal mode transformation parts of *fix pimd/langevin* are written based on
+those of *fix pimd/nvt*, but are significantly revised.
+
 Restart, fix_modify, output, run start/stop, minimize info
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