Initial proposal for SMILES property (Materials-Consortia#368).

optimade.rst

@@ -1988,6 +1988,20 @@ chemical\_formula\_anonymous
 
   - A filter that matches an exactly given formula is :filter:`chemical_formula_anonymous="A2B"`.
 
+smiles
+~~~~~~
+
+- **Description**: The SMILES descriptor for the structure.
+- **Type**: string
+- **Requirements/Conventions**:
+
+  - **Support**: OPTIONAL support in implementations, i.e., MAY be :val:`null`.
+  - **Query**: Support for queries on this property is OPTIONAL.
+    Queries MUST treat the value of this property as a string, not the represented chemical structure.
+    That is, providers MUST NOT perform substructure search, just regular string comparison.
+  - MUST adhere to the `OpenSMILES specification v1.0 <http://opensmiles.org/opensmiles.html>`__.
+  - When structures or their parts cannot be unambiguously depicted in SMILES according to OpenSMILES recommendations, using the guidelines from `Quirós et al. <2018https://jcheminf.biomedcentral.com/articles/10.1186/s13321-018-0279-6>`__ is RECOMMENDED.
+
 dimension\_types
 ~~~~~~~~~~~~~~~~