[Pw_forum] Allowed symmetries in GIPAW
jn336 at cam.ac.uk
Mon Jul 10 10:47:59 CEST 2017
Thanks very much for your explanation.
Could I check one further example with you. This one is (x,y,z) =>
(-x,y,-z), but, it has a fractional translation as well:
isym = 3 180 deg rotation - cart. axis [0,1,0]
cryst. s( 3) = ( 0 -1 0 ) f =( -0.5000000 )
( -1 0 0 ) ( -0.5000000 )
( 0 0 -1 ) ( -0.5000000 )
cart. s( 3) = ( -1.0000000 0.0000000 0.0000000 ) f =( -0.3026487 )
( 0.0000000 1.0000000 0.0000000 ) ( 0.0000000 )
( 0.0000000 0.0000000 -1.0000000 ) ( -0.4029274 )
Would this be allowed in GIPAW?
University of Cambridge
On 2017-07-08 14:41, Davide Ceresoli wrote:
> Dear Joseph,
> that operation is allowed because x=>x, y=>-y, z=>-z,
> if I read correctly. The cartesian matrices can be off
> diagonal. For example the rotation of 90° along z, is also
> allowed, because the triplet (x,y,z) => (-y,x,z) is still
> parallel to the original.
> Basically the problems are with hexagonal crystals and
> with system with very low symmetry.
> For hexagonal crystals, it's better to use ibrav=0, and
> set a,b in the xy plane, c//z, a forming an angle of 30°
> with x.
> In all other cases, if unsure, set nosym=.true. in the SCF
> Best wishes,
> On 07/07/2017 12:35 PM, J. Nelson wrote:
>> Dear all QE users,
>> I am using QE-6.1.
>> The user guide for GIPAW explains that 'symmetry operations that do
>> not map
>> cartesian axes are not allowed (i.e. 120 deg. rotations)'.
>> Does this mean that the Cartesian rotation matrices for each symmetry
>> - e.g.:
>> isym = 4 180 deg rotation - cart. axis [1,0,0]
>> cryst. s( 4) = ( 0 1 0 )
>> ( 1 0 0 )
>> ( 0 0 -1 )
>> cart. s( 4) = ( 1.0000000 0.0000000 0.0000000 ) [<--this
>> matrix here]
>> ( 0.0000000 -1.0000000 0.0000000 )
>> ( 0.0000000 0.0000000 -1.0000000 )
>> need to be diagonal for the symmetry operation to be compatible with
>> GIPAW? Are
>> symmetry operations with an associated fractional translation allowed?
>> Many thanks,
>> Joseph Nelson
>> TCM Group
>> Cavendish Laboratory
>> University of Cambridge
More information about the users