From 9f01fdbb0d0cfa03f346f620ad388ff4d5cd06ba Mon Sep 17 00:00:00 2001
From: Qiming <qiming@flexcompute.com>
Date: Fri, 23 Aug 2024 13:58:21 -0400
Subject: [PATCH] Errored out Bloch boundaries in 2d sims

---
 CHANGELOG.md                    |  1 +
 tidy3d/components/simulation.py | 11 ++++++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e7249beae..d86291be4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 - `PolySlab` now raises error when differentiating and dilation causes damage to the polygon.
+- Validator `boundaries_for_zero_dims` to raise error when Bloch boundaries are used along 0-sized dims.
 
 ### Fixed
 - `DataArray` interpolation failure due to incorrect ordering of coordinates when interpolating with autograd tracers.
diff --git a/tidy3d/components/simulation.py b/tidy3d/components/simulation.py
index 9cb64d822..33d5f368d 100644
--- a/tidy3d/components/simulation.py
+++ b/tidy3d/components/simulation.py
@@ -2410,7 +2410,7 @@ def tfsf_with_symmetry(cls, val, values):
     @pydantic.validator("boundary_spec", always=True)
     @skip_if_fields_missing(["size", "symmetry"])
     def boundaries_for_zero_dims(cls, val, values):
-        """Error if absorbing boundaries, unmatching pec/pmc, or symmetry is used along a zero dimension."""
+        """Error if absorbing boundaries, bloch boundaries, unmatching pec/pmc, or symmetry is used along a zero dimension."""
         boundaries = val.to_list
         size = values.get("size")
         symmetry = values.get("symmetry")
@@ -2420,6 +2420,7 @@ def boundaries_for_zero_dims(cls, val, values):
             if size_dim == 0:
                 axis = axis_names[dim]
                 num_absorbing_bdries = sum(isinstance(bnd, AbsorberSpec) for bnd in boundary)
+                num_bloch_bdries = sum(isinstance(bnd, BlochBoundary) for bnd in boundary)
 
                 if num_absorbing_bdries > 0:
                     raise SetupError(
@@ -2428,6 +2429,14 @@ def boundaries_for_zero_dims(cls, val, values):
                         f"Use either 'Periodic' or 'BlochBoundary' along {axis}."
                     )
 
+                if num_bloch_bdries > 0:
+                    raise SetupError(
+                        f"The simulation has zero size along the {axis} axis, "
+                        "using a Bloch boundary along such an axis is not supported because of "
+                        "the Bloch vector definition in units of '2 * pi / (size along dimension)'. Use a small "
+                        "but nonzero size along the dimension instead."
+                    )
+
                 if symmetry_dim != 0:
                     raise SetupError(
                         f"The simulation has zero size along the {axis} axis, so "