Don't call a subprocess with Q-Chem Custodian (#1851)

## Summary of Changes

Call Custodian directly rather than via a subprocess for Q-Chem.

Requires:
- materialsproject/custodian#323
- Custodian > 2024.2.15

### Checklist

- [X] I have read the ["Guidelines"
section](https://quantum-accelerators.github.io/quacc/dev/contributing.html#guidelines)
of the contributing guide. Don't lie! 😉
- [X] My PR is on a custom branch and is _not_ named `main`.
- [X] I have added relevant, comprehensive [unit
tests](https://quantum-accelerators.github.io/quacc/dev/contributing.html#unit-tests).

### Notes

- Your PR will likely not be merged without proper and thorough tests.
- If you are an external contributor, you will see a comment from
[@buildbot-princeton](https://github.com/buildbot-princeton). This is
solely for the maintainers.
- When your code is ready for review, ping one of the [active
maintainers](https://quantum-accelerators.github.io/quacc/about/contributors.html#active-maintainers).

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/quacc/calculators/qchem/qchem.py

@@ -2,14 +2,10 @@
 
 from __future__ import annotations
 
-import inspect
-import sys
-from pathlib import Path
 from typing import TYPE_CHECKING
 
 from ase.calculators.calculator import FileIOCalculator
 
-from quacc.calculators.qchem import qchem_custodian
 from quacc.calculators.qchem.io import read_qchem, write_qchem
 from quacc.calculators.qchem.params import cleanup_attrs, make_qc_input
 from quacc.calculators.qchem.qchem_custodian import run_custodian
@@ -242,14 +238,11 @@ def __init__(
         # Set default params
         self._set_default_params()
 
-        # Get Q-Chem executable command
-        command = self._manage_environment()
-
         # Instantiate the calculator
         super().__init__(
             restart=None,
             label=None,
-            command=command,
+            command="",
             atoms=self.atoms,
             profile=None,
             **self.fileiocalculator_kwargs,
@@ -287,8 +280,7 @@ def write_input(
             prev_orbital_coeffs=self.prev_orbital_coeffs,
         )
 
-    @staticmethod
-    def execute() -> int:
+    def execute(self) -> int:
         """
         Execute Q-Chem.
 
@@ -298,7 +290,7 @@ def execute() -> int:
             The return code.
         """
 
-        run_custodian()
+        run_custodian(directory=self.directory)
         return 0
 
     def read_results(self) -> None:
@@ -314,19 +306,6 @@ def read_results(self) -> None:
         self.results = results
         self.prev_orbital_coeffs = prev_orbital_coeffs
 
-    @staticmethod
-    def _manage_environment() -> str:
-        """
-        Return the command to run the Q-Chem calculator via Custodian.
-        Returns
-        -------
-        str
-            The command flag to run Q-Chem with Custodian.
-        """
-
-        qchem_custodian_script = Path(inspect.getfile(qchem_custodian)).resolve()
-        return f"{sys.executable} {qchem_custodian_script}"
-
     def _set_default_params(self) -> None:
         """
         Store the parameters that have been passed to the Q-Chem calculator in

src/quacc/calculators/qchem/qchem_custodian.py

@@ -25,6 +25,7 @@ def run_custodian(
     qchem_use_error_handlers: bool | None = None,
     qchem_custodian_max_errors: int | None = None,
     qchem_nbo_exe: str | Path | None = None,
+    directory: str | Path = "./",
 ) -> Popen:
     """
     Function to run QChem Custodian.
@@ -45,6 +46,8 @@ def run_custodian(
         in settings.
     qchem_nbo_exe
         The full path to the NBO executable.
+    directory
+        The runtime directory.
 
     Returns
     -------
@@ -94,6 +97,7 @@ def run_custodian(
         jobs,
         max_errors=qchem_custodian_max_errors,
         terminate_on_nonzero_returncode=False,
+        directory=directory,
     )
 
     return c.run()