[CP2K-user] [CP2K:18170] CELL_OPT

alberto albesantonocito at gmail.com
Sat Dec 10 11:36:45 UTC 2022

Hello cp2k users,
I want to study a crystal of YAG (Y3Al5O12) doped with Yb3 +.

The cation Yb(III) tends to replace Y(III), since the two cations have very 
similar ionic radii.
Hence Yb (III)   occupies the dodecahedral sites of the crystal.
However, in the scientific literature it is hypothesized that a small 
percentage of doping Yb(III)   can occupy the octahedral sites, i.e. 
Yb(III)   replaces Al(III)   cations.
This hypothesis is supported by recent spectroscopic evidence. The 
experimental data are present in the article 

To simulate the distortions of the structure when Yb(III) occupies an 
octahedral site I started from the YAG cubic cell containing 160 atoms and 
replaced an octahedral Al(III) with Yb(III).

I managed to optimize the structure with the LDA functional, while with the 
PBE functional after 53 cycles the calculation did not converge.

I would like to optimize the structure with PBE to subsequently perform a 
pDos calculation and find the splitting of the 4f orbitals of Yb(III) when 
it is in the octahedral site and see if they are comparable with those 
shown in the image below
[image: Yb_YAG_splitting_orbitals.jpg]
What can I improve in the input or what is wrong??

I share input and post the final part of output (file too big)


 ENERGY| Total FORCE_EVAL ( QS ) energy [a.u.]:           

 ENERGY| Total FORCE_EVAL ( QS ) energy [a.u.]:           

 --------  Informations at step =    55 ------------
  Optimization Method        =                 BFGS
  Total Energy               =     -2786.7151034661
  Internal Pressure [bar]    =      -804.8902015897
  Real energy change         =        -0.0000086535
  Predicted change in energy =        -0.0000022936
  Scaling factor             =         0.0309001301
  Step size                  =         0.0011175379
  Trust radius               =         0.4724315332
  Decrease in energy         =                   NO
  Used time                  =             1219.940

  Convergence check :
  Max. step size             =         0.0011175379
  Conv. limit for step size  =         0.0030000000
  Convergence in step size   =                  YES
  RMS step size              =         0.0001385820
  Conv. limit for RMS step   =         0.0015000000
  Convergence in RMS step    =                  YES
  Max. gradient              =         0.0037177331
  Conv. limit for gradients  =         0.0004500000
  Conv. for gradients        =                   NO
  RMS gradient               =         0.0002540531
  Conv. limit for RMS grad.  =         0.0003000000
  Conv. in RMS gradients     =                  YES
  Pressure Deviation [bar]   =      -805.9034515897
  Pressure Tolerance [bar]   =       100.0000000000
  Conv. for  PRESSURE        =                   NO
 Estimated peak process memory after this step [MiB]                       

Thank you

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