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--- faq:hfx_eps_warning [2016/01/22 12:45] – [What should I do when I see this warning message] ltong
+++ faq:hfx_eps_warning [2023/09/26 12:50] (current) – old revision restored (2023/09/25 19:27) bsertcan
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 ====== I received a warning message about the Kohn Sham matrix not 100% occupied when doing Hartree-Fock or hybrid calculations, what is going on, and what should I do?  ======
+<note important> **Since version 2023.2** The occupancy of the Kohn-Sham matrix depends on whether atomic pairs are neighbours. Two atoms are considered neighbours if their basis functions (Gaussians) are overlapping, which is controlled through the ''EPS_PFG_ORB'' keyword. In large cells, the KS matrix can be sparse because atomic pairs can be further apart. Setting the ''MIN_PAIR_LIST_RADIUS'' to -1 makes sure all atomic pairs within the unit cell are considered neighbours, therefore ensuring a full KS matrix. This is considerably more efficient than reducing ''EPS_PFG_ORB'' to unreasonably small numbers. </note>
 When you do a calculation that involves the calculation of the Hartree-Fock exchange (e.g. calculations with hybrid functionals, including using the ADMM method), you may occasionally encounter the following warning message (more often if ADMM is used):
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 <code>
 The Kohn Sham matrix is not 100% occupied.
-This may result in uncorrect Hartree-Fock results.
+This may result in incorrect Hartree-Fock results.
-Try to decrease EPS_PGF_ORB and EPS_FILTER_MATRIX
+Setting MIN_PAIR_LIST_RADIUS to -1 in the QS section
-in the QS section.
+ensures a fully occupied KS matrix.
 </code>