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Next: 2000-04-06: supercell calculation Up: simulation in ceria-zirconia mixed Previous: 2000-03-07: using instead of


2000-04-03: $Ce_{26}M_{6}O_{61}(V_{O}^{\cdot \cdot })_3$ supercell calculation

GOAL

Supercell calculation to see if it makes any difference wrt the mean field approach.

Layout

The water incorporation reaction is decomposed in the following way:

\begin{eqnarray*} H_2O_{(g)}+O^{2-}_{(g)}=2OH^-_{(g)}&&E_{PT}\\ 2OH^-_{(g)}+V_{... ...}^{\cdot\cdot}+O_O^\times=2OH_{O}^\cdot&&E_{H_2O}=E_{PT}+E_{2OH} \end{eqnarray*}



The $E_{2OH}$ term is evaluated in a single GULP run, by setting up a supercell and a suitable defect description.

The protocol is as follows.

  1. generate a supercell with genlat from the DL_POLY distribution
  2. generate a random distribution of the proper number of dopant ions and oxygen vacancies with the dlsub code
  3. bulk optimize the supercell without symmetry ( space 1)
  4. set up the defect corresponding to the above reaction with the gulpdb code. Basically: 

    
impurity         O2     core   cart   10.1117    7.48665    4.72921   
interstitial     O2     core   cart   1.99447    4.85917    7.56852   
interstitial     H2     core   cart   2.52745    4.28948    8.11063   
interstitial     H2     core   cart   9.56649    6.94671    5.2893

    The above means: substitute an oxide ion with an $OH$ oxygen ( O2 species), put an $OH$ oxygen at an oxygen vacancy (the interstitial O2 directive), insert the necessary $H$'s to make up the two $OH$ groups.

Results

\begin{center} \begin{threeparttable} \begin{tabular}{lD{.}{.}{6}D{.}{.}{1}D{.}{... ...See also the abnormal CPU time. \end{tablenotes}\end{threeparttable}\end{center}

\begin{center} \begin{threeparttable} \begin{tabular}{lD{.}{.}{6}D{.}{.}{6}D{.}{... ....410111 & 13.937507 & 2.167507 \\ \end{tabular}\end{threeparttable}\end{center}

\begin{center}\vbox{\input{2000-04-03-01.pslatex} }\end{center}

Apart from the two abnormally low values for $Gd$ and $Y$, the trend is still in contrast with the experimental results of Sakai et al. (1999)

Final $OH$ geometry

The starting $OH$ orientation was along the [111] crystallographic direction. This orientation did not change after relaxation in all cases.

Representative input files

Bulk optimization 


opti conp
dump every 1 01-yb-bulk.dump
maxcyc  200
cutb 3.0 # what does this mean? Ronny uses it.
title
Ytterbium solid solution
N.Sakai et al. Solid State Ionics 125(1999)325-331
end
cell
10.80137600  10.80137600  10.80137600  90.0 90.0 90.0

fractional
Yb     core   0.81250000  0.31250000  0.56250000    3.00000000 1.00000 0.00000 
Yb     core   0.56250000  0.31250000  0.81250000    3.00000000 1.00000 0.00000 
Yb     core   0.06250000  0.06250000  0.56250000    3.00000000 1.00000 0.00000 
Yb     core   0.56250000  0.81250000  0.31250000    3.00000000 1.00000 0.00000 
Yb     core   0.06250000  0.06250000  0.06250000    3.00000000 1.00000 0.00000 
Yb     core   0.06250000  0.31250000  0.31250000    3.00000000 1.00000 0.00000 
Ce4    core   0.56250000  0.56250000  0.56250000    -3.7000000 1.00000 0.00000 
...    ...    ....        ....        ....          ....       ....    .... 
O1     shel   0.18750000  0.43750000  0.18750000    -2.0769999 1.00000 0.00000 
O1     shel   0.18750000  0.18750000  0.43750000    -2.0769999 1.00000 0.00000 
O1     shel   0.43750000  0.43750000  0.43750000    -2.0769999 1.00000 0.00000 
O1     shel   0.18750000  0.43750000  0.43750000    -2.0769999 1.00000 0.00000 

space
1

#########################
# Shell-core charges
#########################
species   
Ce3   shel    7.700000
Ce3   core   -4.700000   
O2    core   -1.4263
H2    core    0.4263         
#########################
# Short range potentials
#########################
buck 
Ce4 shel O1 shel    1986.830000 0.351070   20.40000  0.0 15.000
Ce3 shel O1 shel    1731.61808  0.36372    14.43256  0.0 15.000
Yb  core O1 shel    1309.6      0.34620     0.00000  0.0 15.0
O1  shel O1 shel   22764.300000 0.149000   27.89000  0.0 15.000
O2  core O1 shel   22764.300000 0.149000   27.89000  0.0 15.000
H2  core O1 shel     311.970    0.25        0.0      0.0 15.000
Ce4 shel O2 core    1986.830000 0.351070   20.40000  0.0 15.000
Yb  core O2 core    1309.6      0.34620     0.00000  0.0 15.0
morse
H2  core O2 core       7.05250  2.19860     0.9485   1.0 0.0 2.0
#########################
# Spring parameters
#########################
spring 
Ce4    291.750000
Ce3    291.750000
O1      27.29

Defect calculation 


# 
# Keywords:
# 
opti conp bulk_noopt defect regi_before nodsymmetry
# 
# Options:
# 
title
Yttrium solid solution                                                          
N.Sakai et al. Solid State Ionics 125(1999)325-331                              
end
cell
  10.857114  10.866269  10.864256  89.792860  89.883623  89.738476
fractional  180
Y     core 0.8125000 0.3125000 0.5625000 3.00000000 1.00000 0.00000             
Y     core 0.5556062 0.3118786 0.8249504 3.00000000 1.00000 0.00000             
Y     core 0.0439579 0.0622810 0.5603046 3.00000000 1.00000 0.00000             
Y     core 0.5513066 0.8081226 0.3109349 3.00000000 1.00000 0.00000             
...   ...  ....      ....      ....      ....       ....    .... 
O1    shel 0.1805190 0.4399801 0.1877716 -2.0769998 1.00000 0.00000             
O1    shel 0.2179040 0.1859991 0.4404767 -2.0769998 1.00000 0.00000             
O1    shel 0.4311125 0.4093523 0.4410598 -2.0769998 1.00000 0.00000             
O1    shel 0.1854540 0.4476465 0.4760760 -2.0769998 1.00000 0.00000             

size   10.7    20.00
center                         cart   6.05003    5.8955     6.42442   
impurity         O2     core   cart   10.1117    7.48665    4.72921   
interstitial     O2     core   cart   1.99447    4.85917    7.56852   
interstitial     H2     core   cart   2.52745    4.28948    8.11063   
interstitial     H2     core   cart   9.56649    6.94671    5.2893    


space
  1
species   9
Ce3    shel    7.700000            
Ce3    core   -4.700000            
O2     core   -1.426300            
H2     core    0.426300            
Y      core    3.000000            
Ce4    core   -3.700000            
O1     core    0.077000            
Ce4    shel    7.700000            
O1     shel   -2.077000            
buck     
O1    shel Ce4   shel  1986.8300     0.351070 20.400      0.000 15.000
buck     
O1    shel Ce3   shel  1731.6181     0.363720 14.433      0.000 15.000
buck     
Y     core O1    shel  1345.1000     0.349100 .00000E+00  0.000 15.000
buck     
O1    shel O1    shel  22764.300     0.149000 27.890      0.000 15.000
buck     
O2    core O1    shel  22764.300     0.149000 27.890      0.000 15.000
buck     
H2    core O1    shel  311.97000     0.250000 .00000E+00  0.000 15.000
buck     
O2    core Ce4   shel  1986.8300     0.351070 20.400      0.000 15.000
buck     
O2    core Y     core  1345.1000     0.349100 .00000E+00  0.000 15.000
morse     
H2    core O2    core 7.0525000     2.1986      0.94850  1.0000  2.000
spring
Ce4    291.75000    
spring
Ce3    291.75000    
spring
O1     27.290000    
cutd   3.0000
maxcyc opt      200
maxcyc fit      200
dump every   1 02-y-OH.dump

next up previous contents
Next: 2000-04-06: supercell calculation Up: simulation in ceria-zirconia mixed Previous: 2000-03-07: using instead of