From 8e109ae12a62146017e59a672a641f53938d9891 Mon Sep 17 00:00:00 2001
From: Murali <muralidharrsvm7@gmail.com>
Date: Thu, 14 May 2026 11:26:41 +0200
Subject: [PATCH] update citation, remove wrong warning in exciton symmeties,
 add notes in exc_mat_elemets function

---
 yambopy/bse/exciton_irreps.py          |  6 +++---
 yambopy/bse/exciton_matrix_elements.py | 17 +++++++++++++++++
 yambopy/bse/rotate_excitonwf.py        |  4 ++--
 yambopy/dbs/wfdb.py                    |  4 ++--
 4 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/yambopy/bse/exciton_irreps.py b/yambopy/bse/exciton_irreps.py
index c2845845..ee1c39d9 100644
--- a/yambopy/bse/exciton_irreps.py
+++ b/yambopy/bse/exciton_irreps.py
@@ -12,7 +12,7 @@
 from yambopy.symmetries.crystal_symmetries import Crystal_Symmetries
 from yambopy.tools.citations import citation
 
-@citation("M. Nalabothula et al. arXiv:2511.21540 (2025)")
+@citation("M. Nalabothula et al.: Phys. Rev. B 113, 205130 (2026)")
 def compute_exc_rep(path='.', bse_dir='SAVE', iqpt=1, nstates=-1, degen_tol = 1e-3,
                     degen_rtol=1e-3, symm_tol=1e-2, use_save_symmetries=False):
     """
@@ -134,9 +134,9 @@ def compute_exc_rep(path='.', bse_dir='SAVE', iqpt=1, nstates=-1, degen_tol = 1e
     ## for q = 0, Lkind = "bar" is recommended as "full" will 
     ## break symmetries (depends on the chosen direction)
     if excdb.Lkind is not None: # compatibility with old databases
-        if iqpt==0 and 'bar' not in excdb.Lkind:
+        if iqpt==1 and 'bar' not in excdb.Lkind:
             print(f"Warning: You are using Lkind={excdb.Lkind} at q=0, but 'Lbar' is recommended. Symmetries are broken in this way.")
-        if iqpt!=0 and 'full' not in excdb.Lkind:
+        if iqpt > 1 and 'full' not in excdb.Lkind:
             print(f"Warning: You are using Lkind={excdb.Lkind} at q!=0, but 'Lfull' should be used.")
 
     # Load the wavefunction database
diff --git a/yambopy/bse/exciton_matrix_elements.py b/yambopy/bse/exciton_matrix_elements.py
index 1da816ca..35e62067 100644
--- a/yambopy/bse/exciton_matrix_elements.py
+++ b/yambopy/bse/exciton_matrix_elements.py
@@ -20,6 +20,23 @@ def exciton_X_matelem(exe_kvec, O_qvec, Akq, Ak, Omn, kpts, contribution='b', di
     discarding the third term (disconnected diagram). The calculation is performed in the
     Tamm-Dancoff approximation.
 
+    Here we follow k-Q -> k for electronic transitions (backward convention),
+    while using k -> k+q for O(q) matrix elements (forward convention).
+    So this is mixed convention as given in
+    Eq. D8 of M. Nalabothula et al.: Phys. Rev. B 113, 205130 (2026)
+
+    Other conventions see (not used here)
+    Both Forward :
+        H.-Y. Chen et al.: Phys. Rev. Lett. 125, 107401 (2020)
+        G. Antonius et al.: Phys. Rev. B 105, 085111 (2022)
+    Both Backward :
+        F. PALEARI, PhD thesis
+        M. Zanfrognini et al.: Phys. Rev. Lett. 131, 206902 (2023)
+        P. Lechifflart et al.: Phys. Rev. Mater. 7, 024006 (2023)
+
+    Note: Different conventions correspond to different ways of writing the
+          the same matrix elements.
+
     Parameters
     ----------
     exe_kvec : array_like
diff --git a/yambopy/bse/rotate_excitonwf.py b/yambopy/bse/rotate_excitonwf.py
index 0d5e8bff..f2a1f8e7 100644
--- a/yambopy/bse/rotate_excitonwf.py
+++ b/yambopy/bse/rotate_excitonwf.py
@@ -7,7 +7,7 @@
 
 
 @func_profile
-@citation("M. Nalabothula et al. arXiv:2511.21540 (2025)")
+@citation("M. Nalabothula et al.: Phys. Rev. B 113, 205130 (2026)")
 def rotate_exc_wf(Ak, symm_mat_red, kpoints, exe_qpt, dmats, time_rev, ktree=None):
     """
     Rotate the exciton wavefunction Ak using symmetry operations.
@@ -16,7 +16,7 @@ def rotate_exc_wf(Ak, symm_mat_red, kpoints, exe_qpt, dmats, time_rev, ktree=Non
     which is represented in the basis of electronic states. The rotation is
     performed using the symmetry matrix in reduced coordinates and the
     corresponding representation matrices.
-    Implements Eq. (49) of M. Nalabothula et al. arXiv:2511.21540 (2025)
+    Implements Eq. (49) of M. Nalabothula et al.: Phys. Rev. B 113, 205130 (2026)
 
     Parameters
     ----------
diff --git a/yambopy/dbs/wfdb.py b/yambopy/dbs/wfdb.py
index 42627633..c424dc4d 100644
--- a/yambopy/dbs/wfdb.py
+++ b/yambopy/dbs/wfdb.py
@@ -531,11 +531,11 @@ def get_BZ_wf(self, ik):
 
 
     @func_profile
-    @citation("M. Nalabothula et al. arXiv:2511.21540 (2025)")
+    @citation("M. Nalabothula et al.: Phys. Rev. B 113, 205130 (2026)")
     def Dmat(self, symm_mat=None, frac_vec=None, time_rev=None):
         """
         Computes the symmetry-adapted matrix elements < Rk | U(R) | k >.
-        Implements Eq. 5 of M Nalabothula et al. arXiv:2511.21540.
+        Implements Eq. 5 of M. Nalabothula et al.: Phys. Rev. B 113, 205130 (2026).
 
         Parameters
         ----------