From b98d02bce2a8a98cb8d72855df56f1af7ae48702 Mon Sep 17 00:00:00 2001
From: Alexander Holas <alex.holas@gmx.de>
Date: Wed, 1 Nov 2023 16:57:25 -0400
Subject: [PATCH] Fix deprecated series index

---
 tardis/plasma/properties/nlte_rate_equation_solver.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tardis/plasma/properties/nlte_rate_equation_solver.py b/tardis/plasma/properties/nlte_rate_equation_solver.py
index e3be83c383c..487b93ad5a3 100644
--- a/tardis/plasma/properties/nlte_rate_equation_solver.py
+++ b/tardis/plasma/properties/nlte_rate_equation_solver.py
@@ -595,7 +595,7 @@ def prepare_first_guess(
         """
         first_guess = pd.Series(0.0, index=rate_matrix_index)
         for atomic_number in atomic_numbers:
-            first_guess.loc[(atomic_number, 1)][0] = number_density.loc[
+            first_guess.loc[(atomic_number, 1)].iloc[0] = number_density.loc[
                 atomic_number
             ]
         # TODO: After the first iteration, the new guess can be the old solution.