Added an example of the direct calculator with metatensor

examples/clients/metatensor/README.md

@@ -10,14 +10,14 @@ machine learning potentials.
 
 ## Installation
 
-The code is compatible with metatensor-torch v0.5, which you can install with
+The code is compatible with metatensor-torch v0.6, which you can install with
 
 ```bash
 # install all metatensor packages simultaneously
 pip install "metatensor[torch]"
 
 # install packages individually, with explicit control over the installed versions
-pip install "metatensor-torch ==0.5.*" "metatensor-operations ==0.2.*"
+pip install "metatensor-torch ==0.6.*" "metatensor-operations ==0.2.*"
 ```
 
 ## Running the example
@@ -42,3 +42,13 @@ The options (after `-o`) are as follow:
 - `check_consistency` controls whether we should run some extra internal
   consistency checks about data given to the model and data returned by the
   model.
+
+## Running with FFDirect 
+
+It is also possible to run the metatensor PES directly, without the need for an external
+driver. To do so, you need to use a `<ffdirect>` clause in the input, and specify
+the appropriate options as a dictionary. Then, you can simply run
+
+```bash
+i-pi input-direct.xml
+``` 

examples/clients/metatensor/input-direct.xml

@@ -0,0 +1,47 @@
+<simulation verbosity="medium">
+<output prefix="lj-nickel">
+    <properties stride="5" filename="out">
+		[step, time{picosecond}, conserved{electronvolt}, temperature{kelvin},
+		kinetic_md{electronvolt}, potential{electronvolt}, pressure_md{bar},
+		volume{angstrom3}, ensemble_temperature{kelvin}, cell_abcABC]
+    </properties>
+    <trajectory filename="xc" stride="5" cell_units="angstrom"> x_centroid{angstrom} </trajectory>
+    <checkpoint stride="1000"/>
+</output>
+<total_steps> 1000</total_steps>
+<prng><seed>12345</seed></prng>
+
+<ffdirect name='driver'>
+    <pes> metatensor </pes>
+    <parameters> {template:nickel.xyz,model:nickel-lj.pt,device:cpu } </parameters>
+</ffdirect>
+
+<system>
+    <initialize nbeads="1">
+        <file mode="ase" units="angstrom"> nickel.xyz </file>
+        <velocities mode="thermal" units="kelvin"> 250.0 </velocities>
+    </initialize>
+    <forces>
+    	<force forcefield='driver'/>
+    </forces>
+
+    <motion mode="dynamics">
+    	<dynamics mode="nvt">
+        	<timestep units="femtosecond"> 0.5 </timestep>
+            <thermostat mode='gle'>
+            	<A shape='(5,5)'>[
+                	 4.49e-3,   6.59e-6,   2.79e-4,  -8.81e-4,   5.61e-3,
+                    -6.73e-6,   2.08e-9,   1.75e-5,  -4.80e-6,   1.03e-5,
+                    -3.59e-4,  -1.75e-5,   3.29e-5,   1.24e-4,  -2.42e-4,
+                    -2.51e-4,   4.80e-6,  -1.24e-4,   6.45e-4,   2.78e-4,
+                     5.27e-3,  -1.03e-5,   2.42e-4,  -2.78e-4,   7.49e-3
+                ]</A>
+            </thermostat>
+        </dynamics>
+    </motion>
+
+	<ensemble>
+        <temperature units="kelvin"> 250.0 </temperature>
+    </ensemble>
+</system>
+</simulation>

ipi/engine/forcefields.py

@@ -424,7 +424,11 @@ def __init__(
         self.driver = __drivers__[self.pes](verbose=verbosity.high, **pars)
 
     def evaluate(self, request):
-        request["result"] = list(self.driver(request["cell"][0], request["pos"]))
+        results = list(self.driver(request["cell"][0], request["pos"].reshape(-1, 3)))
+        # ensure forces and virial have the correct shape
+        results[1] = results[1].reshape(-1)
+        results[2] = results[2].reshape(3, 3)
+        request["result"] = results
         request["status"] = "Done"