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[Anurag Chaudhry <anuragchaudhry@yahoo.co.uk>]

Hello,

I wanted to ask few question about cell relaxation.  For some compounds I wish to calculate I do not have the exact space group and atomic positions so at times I take an iso-structural cell and relax the cell with "optcell 2" and specify a dilatmx value (also ionmov 2).  But I see that abinit relaxes the lattice vectors (a,b,c) and also the angles alpha,beta, gamma.  could you explain how beneficial it is use changed alpha/beta/gamma values in addition to the lattice vectors ?  I was using the changed lattice vectors but original angles.

I am not quite sure if I understand the guidelines on the abinit webpage regarding "It is STRONGLY suggested first to optimize the ionic positions without cell shape and size optimization (optcell=0), then start the cell shape and size optimization from the cell with relaxed ionic positions."  Should I be doing a ionic position optimization (optcell 0) before optcell 2 ?

Since ultimately I am interested to dope the material (replace one cation with a isovalent dopant ion) later on so I was wondering how much beneficial it is to follow the above mentioned recipe.  When I relax the structure with a dopant I only do ionic position relaxation (ionmov 2) keeping the cell volume constant (optcell 0).

thank you for your time and help.

regards,
Anurag

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