QCQMC part 3: Add Hamiltonian (#345)

Adds hamiltonian module for specifying a second quantized hamiltonian used for optimizing a trial wavefunction.

recirq/qcqmc/data.py

@@ -13,36 +13,43 @@
 # limitations under the License.
 
 import abc
-import dataclasses
 import hashlib
 import pathlib
-from dataclasses import dataclass
 from pathlib import Path
 
+import attrs
 import numpy as np
 
 DEFAULT_BASE_DATA_DIR = (Path(__file__).parent / "data").resolve()
 
 
 def get_integrals_path(
-    name: str, *, base_data_dir: str = DEFAULT_BASE_DATA_DIR
+    name: str, *, base_data_dir: pathlib.Path = DEFAULT_BASE_DATA_DIR
 ) -> Path:
     """Find integral data file by name.
 
     Args:
         name: The molecule name.
+        base_data_dir: The base directory where the data folder should live.
     """
-    return Path(base_data_dir) / "integrals" / name / "hamiltonian.chk"
+    return base_data_dir / "integrals" / name / "hamiltonian.chk"
 
 
 _MOLECULE_INFO = {"fh_sto3g"}
 
 
 # should go in Dedicated module
-@dataclass(frozen=True, repr=False)
+@attrs.frozen
 class Params(abc.ABC):
+    """Store named parameters which will potentiall be read from a file.
+
+    Args:
+        name: The name of the parameters
+    """
+
     name: str
 
+    # TODO: Is this necessary?
     def __eq__(self, other):
         """A helper method to compare two dataclasses which might contain arrays."""
         if self is other:
@@ -53,9 +60,7 @@ def __eq__(self, other):
 
         return all(
             array_compatible_eq(thing1, thing2)
-            for thing1, thing2 in zip(
-                dataclasses.astuple(self), dataclasses.astuple(other)
-            )
+            for thing1, thing2 in zip(attrs.astuple(self), attrs.astuple(other))
         )
 
     @property
@@ -78,7 +83,7 @@ def __repr__(self):
         # This custom repr lets us add fields with default values without changing
         # the repr. This, in turn, lets us use the hash_key reliably even when
         # we add new fields with a default value.
-        fields = dataclasses.fields(self)
+        fields = attrs.fields(self)
         # adjusted_fields = [f for f in fields if getattr(self, f.name) != f.default]
         adjusted_fields = [
             f
@@ -99,8 +104,14 @@ def _json_namespace_(cls):
 
 
 # Should go in dedicated module
-@dataclass(frozen=True, eq=False)
+@attrs.frozen
 class Data(abc.ABC):
+    """A container for different forms of data used in qcqmc (hamiltonian, trial wavefunction, ...).
+
+    Args:
+        params: The name of the parameters
+    """
+
     params: Params
 
     def __eq__(self, other):
@@ -113,9 +124,7 @@ def __eq__(self, other):
 
         return all(
             array_compatible_eq(thing1, thing2)
-            for thing1, thing2 in zip(
-                dataclasses.astuple(self), dataclasses.astuple(other)
-            )
+            for thing1, thing2 in zip(attrs.astuple(self), attrs.astuple(other))
         )
 
     @classmethod