Add exponential backoff

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: mhucka

src/openfermion/chem/pubchem.py

@@ -38,13 +38,14 @@ def geometry_from_pubchem(name: str, structure: str = None):
 
     def get_compounds_with_retries(name, record_type):
         max_retries = 3
-        delay = 2
+        initial_delay = 1
         for attempt in range(max_retries):
             try:
                 return pubchempy.get_compounds(name, 'name', record_type=record_type)
             except (pubchempy.PubChemHTTPError, urllib.error.URLError):
                 if attempt == max_retries - 1:
                     raise
+                delay = initial_delay * (2 ** attempt)
                 time.sleep(delay)
 
     if structure in ['2d', '3d']: