added check for number of cores available vs needed

src/mindlessgen/generator/main.py

@@ -96,6 +96,12 @@ def generator(config: ConfigManager) -> tuple[list[Molecule], int]:
     exitcode = 0
     optimized_molecules: list[Molecule] = []
 
+    # Assert that parallel configuration is valid 
+    if num_cores < config.refine.ncores:
+        raise RuntimeError(f"Number of cores ({num_cores}) is too low to run refinement using {config.refine.ncores}.")
+    if config.general.postprocess and num_cores < config.postprocess.ncores:
+        raise RuntimeError(f"Number of cores ({num_cores}) is too low to run post-processing using {config.postprocess.ncores}.")
+
     # Initialize parallel blocks here
     blocks = setup_blocks(
         num_cores,