Merge pull request brucefan1983#1303 from brucefan1983/doc-gnep

doc gnep

Author: brucefan1983

doc/installation.rst

@@ -33,6 +33,34 @@ You can find several examples for how to use both the ``gpumd`` and ``nep`` exec
 .. _netcdf_setup:
 .. index::
    single: NetCDF setup
+   
+GNEP setup
+==========
+
+GNEP stands for a method of training NEP models using analytical Gradients (G stands for Gradients).
+See the `implementation paper <https://doi.org/10.1016/j.cpc.2025.109994/>`_ for details.
+
+To compile the ``gnep`` executable, one can run ``make gnep`` in the ``src`` directory.
+
+The usage of the ``gnep`` executable is similar to that of the ``nep`` executable.
+The major difference is that training hyperparameters are written in ``gnep.in`` instead of ``nep.in``'
+Below we use an explicit example with default parameters (except for the ``type`` keyword) to illustrate the inputs in ``gnep.in``::
+
+  type         2 Ge Se      # same usage as in nep.in
+  prediction   0            # same usage as in nep.in
+  cutoff       8 4          # same usage as in nep.in
+  n_max        4 4          # same usage as in nep.in
+  basis_size   8 8          # same usage as in nep.in
+  l_max        4            # same usage as in nep.in but does not support 4-body and 5-body descriptors
+  neuron       30           # same usage as in nep.in
+  lambda_e     1.0          # same usage as in nep.in
+  lambda_f     2.0          # same usage as in nep.in but defaults to 2
+  lambda_v     0.1          # same usage as in nep.in
+  start_lr     1e-3         # new keyword to set the starting learning rate, which should be a non-negative floating-point number
+  stop_lr      1e-7         # new keyword to set the stopping learning rate, which should be a non-negative floating-point number
+  weight_decay 0.0          # new keyword to set the weight decay parameter, which should be a non-negative floating-point number
+  batch        2            # same usage as in nep.in but favors small values
+  epoch        50           # one epoch equals #structures/#batchsize training steps
 
 NetCDF setup
 ============