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<meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">In order to know the symmetry of a structure you do not have to look at the unit cell, but to the symmetry group of the structure. You can have a triclinic structure with a cubic unit cell. Just look at the symmetry group that is indicated in the database, and you will see that its point-group is monoclinic.<div class=""><br class=""></div><div class="">The monoclinic magnetic structure of NiO in the database comes from an experimental report where any deviation of the positional structure and lattice from the parent cubic was considered negligible. As in general the magnetic induced structural distortions are very weak one has to make a specific effort to detect them and to characterize them experimentally (and I suppose also in calculations as explained by Stefaan Cottenier). A rombohedral strain is just a less general strain than a monoclinic one. If the strain is very weak, a first appoximation to it can be a rombohedral strain, which has only one free parameter to determine, instead of the three that requires the monoclinic strain.</div><div class=""><br class=""></div><div class="">best regards,</div><div class=""><br class=""></div><div class="">Manuel</div><div class=""><br class=""></div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">El 10/6/2016, a las 12:48, Abderrahmane Reggad <<a href="mailto:jazairdz@gmail.com" class="">jazairdz@gmail.com</a>> escribió:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><br clear="all" class=""><div class="">Thanks Mr Khan Manuel for your contribution to enrich the subject of geometrical frustration and magnetism .</div><div class=""><br class=""></div><div class="">After reading your contribution, I made the following remarks:</div><div class=""><br class=""></div><div class="">* you have said:<span style="font-family: courier, 'courier new', monospace; font-size: 14px; line-height: 19.6px; white-space: pre-wrap;" class="">In the case of NiO the magnetic </span><span style="font-family: courier, 'courier new', monospace; font-size: 14px; line-height: 19.6px; white-space: pre-wrap;" class="">order reduces the symmetry to monoclinic,</span> but what we know all is that the magnetic order reduces the symmetry in NiO from cubic to rhombohedral.</div><div class=""><br class=""></div><div class="">* From the<span style="font-family: courier, 'courier new', monospace; font-size: 14px; line-height: 19.6px; white-space: pre-wrap;" class="">MAGNDATA database, It's mentionned that the magnetic unit cell is cubic </span></div><div class=""><br class=""></div><div class=""><b style="font-family: arial, verdana, helvetica, sans-serif; font-size: 16px;" class="">Lattice parameters of the magnetic unit cell:</b><br style="font-family: arial, verdana, helvetica, sans-serif; font-size: 16px;" class=""><span style="font-family: arial, verdana, helvetica, sans-serif; font-size: 16px;" class="">8.3500 8.3500 8.3500 90.0000 90.0000 90.0000</span><br class=""></div><div class=""><span style="font-family: arial, verdana, helvetica, sans-serif; font-size: 16px;" class=""><br class=""></span></div><div class=""><span style="font-family: arial, verdana, helvetica, sans-serif; font-size: 16px;" class="">Whould you explain that </span></div><div class=""><span style="font-family: arial, verdana, helvetica, sans-serif; font-size: 16px;" class=""><br class=""></span></div><div class=""><span style="font-family: arial, verdana, helvetica, sans-serif; font-size: 16px;" class="">Best regards</span></div><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div style="font-family:monospace" class=""><div class=""><font size="2" class=""><span style="color:rgb(0,0,255)" class="">Mr: A.Reggad</span> <br class=""><span style="background-color:rgb(238,238,238)" class=""><span style="color:blue" class="">Laboratoire de Génie Physique</span></span><br class=""></font></div><font size="2" class=""><span style="color:rgb(0,0,255)" class="">Université Ibn Khaldoun - Tiaret</span><br class=""></font></div><div class=""><font size="2" class=""><span style="font-family:monospace" class=""><span style="color:rgb(0,0,255)" class="">Algerie</span></span></font><br class=""></div><div class=""><div class=""><br class=""><span style="font-family:"times new roman",serif" class=""><span style="color:blue" class=""></span></span><br class=""></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div>
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<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div class="">**************************************************</div><div class="">J. Manuel Perez-Mato<br class="">Fac. Ciencia y Tecnologia,<br class="">Universidad del Pais Vasco, UPV<br class="">48080 BILBAO,<br class="">Spain<br class=""><br class="">tel. +34 946012473<br class="">fax. +34 946013500<br class="">***************************************************<br class=""></div></span>
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