From tone.kokalj at ijs.si  Mon Dec  2 19:39:06 2024
From: tone.kokalj at ijs.si (Tone Kokalj)
Date: Mon, 02 Dec 2024 19:39:06 +0100
Subject: [QE-developers] ibrav = -3 vs. ibrav = 7
Message-ID: <587bcdc49eab165ea908e6cdf3593accc79ab159.camel@ijs.si>

Dear colleagues,

I spotted the following minor inconsistency between ibrav=-3 and
ibrav=7 primitive vectors:

ibrav = -3, Cubic I (bcc), (more symmetric axes):
??? v1 = (a/2)(-1,1,1), v2 = (a/2)(1,-1,1),? v3 = (a/2)(1,1,-1)

ibrav = 7, Tetragonal I (bct)
??? v1=(a/2)(1,-1,c/a),? v2=(a/2)(1,1,c/a),? v3=(a/2)(-1,-1,c/a)

This implies that -3 and 7 are mutually inconsistent. Perhaps, new
ibrav can be added as:

ibrav = -7 Tetragonal I (bct), (compatible with -3)
??? v1=(a/2)(-1,1,c/a),? v2=(a/2)(1,-1,c/a),? v3=(a/2)(1,1,-c/a)

This new ibrav would aid at automatic conversion from, say, CIF or XSF
to pw.x input with ibrav, celldm(i) & ATOMIC_POSITIONS crystal.

Best regards,
Tone
-- 
Jo?ef Stefan Institute, Ljubljana, Slovenia