ACE mliap examples and virial support

examples/mliap/mliap_pytorch_ACE.py

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+# Demonstrate how to load a model from the python side.
+# This is essentially the same as in.mliap.pytorch.MOF
+# except that python is the driving program, and lammps
+# is in library mode.
+before_loading =\
+"""# Demonstrate MLIAP/PyTorch interface to torch model
+
+# Initialize simulation
+
+variable        nsteps index 100
+variable        nrep equal 4
+variable        a equal 3.316
+units           metal
+
+# generate the box and atom positions using a BCC lattice
+
+variable nx equal ${nrep}
+variable ny equal ${nrep}
+variable nz equal ${nrep}
+
+boundary        p p p
+
+lattice         bcc $a
+region          box block 0 ${nx} 0 ${ny} 0 ${nz}
+create_box      1 box
+create_atoms    1 box
+
+mass 1 180.88
+
+# define potential with LATER mliappy
+
+
+pair_style  mliap model mliappy LATER descriptor ace ccs_single_element.yace
+pair_coeff * * Ta
+
+"""
+after_loading =\
+"""
+
+# Setup output
+
+compute  eatom all pe/atom
+compute  energy all reduce sum c_eatom
+
+compute  satom all stress/atom NULL
+compute  str all reduce sum c_satom[1] c_satom[2] c_satom[3]
+variable press equal (c_str[1]+c_str[2]+c_str[3])/(3*vol)
+
+thermo_style    custom step temp epair c_energy etotal press v_press
+thermo          10
+thermo_modify   norm yes
+
+# Set up NVE run
+dump            1 all cfg 10 ats.*.cfg mass type xs ys zs
+dump_modify     1 element Ta
+
+timestep 0.5e-3
+neighbor 1.0 bin
+neigh_modify once no every 1 delay 0 check yes 
+
+# Run MD
+
+velocity all create 300.0 4928459 loop geom
+fix 1 all nve
+run             ${nsteps}
+"""
+import lammps
+
+lmp = lammps.lammps(cmdargs=['-echo','both'])
+
+# Before defining the pair style, one must do the following:
+import lammps.mliap
+lammps.mliap.activate_mliappy(lmp)
+# Otherwise, when running lammps in library mode,
+# you will get an error:
+# "ERROR: Loading MLIAPPY coupling module failure."
+
+# Setup the simulation and declare an empty model
+# by specifying model filename as "LATER"
+lmp.commands_string(before_loading)
+
+# Define the model however you like. In this example
+# we load it from disk:
+import os
+import torch
+torch_model = 'ACE_NN_Pytorch.pt'
+if not os.path.exists(torch_model):
+    raise FileNotFoundError(f"Generate {torch_model} first")
+model = torch.load(torch_model)
+
+# Connect the PyTorch model to the mliap pair style.
+lammps.mliap.load_model(model)
+
+# run the simulation with the mliap pair style
+lmp.commands_string(after_loading)
+lmp.close()
+lmp.finalize()