Next: 2000-02-25: trying a different Up: simulation in ceria-zirconia mixed Previous: 2000-02-21: with a different

2000-02-23: changing the initial orientation of the group

GOAL

In this series of calculations, the initial orientation of the group was along the crystallographic direction, i.e. along the face diagonal of the cube of oxygen atoms inside the unit cell. Moreover, relaxation of the defect was done without simmetry (i.e. the keyword nodsymmetry was used).

This calculations are to be compared with 2000-02-02 (3), in which the starting orientation of the group was along the direction and symmetry was used for defect relaxation.

Results

$\fbox { \begin{minipage}{0.6\linewidth} \bf Mon Mar 6 18:28:52 2000\\ Mean field correction NOT applied here. See 2000-03-03 \end{minipage}}%\fbox$

Comparison with/without `nodsymmetry` with the same starting orientation

Since here we change two variables (the nodsymmetry keyword and the starting orientation of the group) a question arises as to whether the nodsymmetry keyword makes any difference when the same starting orientation of the group is used.

The following compares results for $Ce_{0.8}Gd_{0.2}O_{1.9}$ mixed oxide using two input files which differ only for the presence of the nodsymmetry keyword (the starting orientation was along the direction in both runs):


dschsun1:147> diff -c gd-OH gd-OH-sym
*** gd-OH       Wed Feb 23 12:39:55 2000
--- gd-OH-sym   Thu Feb 24 10:53:50 2000
***************
*** 1,6 ****
! opti conp defect regi_before nodsymmetry
  #conp defect single
! dump every 1 gd-OH.dump
  maxcyc  200
  cutb 3.0 # what does this mean? Ronny uses it.
  title
--- 1,6 ----
! opti conp defect regi_before
  #conp defect single
! dump every 1 gd-OH-sym.dump
  maxcyc  200
  cutb 3.0 # what does this mean? Ronny uses it.
  title
dschsun1:148>

$\begin{center} \begin{threeparttable} \begin{tabular}{lll} &\multicolumn{1}{c}{w... ...otal CPU time ({$h$})&2.40&1.05\\ \end{tabular}\end{threeparttable}\end{center}$

Apparently, the only thing that changes is the total CPU time, which is more than doubled for the run which uses symmetry for defect relaxation. This is surprising, as I'd expect that use of symmetry would reduce CPU times.

$E_{H_2O}$ evaluation

Details for $E_{H_2O}$ evaluation can be found in 2000-02-02 (3). Potential parameters are the same as that calculation.

$\begin{threeparttable} \begin{tabular}{lD{.}{.}{6}D{.}{.}{6}D{.}{.}{0}D{.}{.}{6}... ...0.2}O_{1.9}$} &5.400688 & 9.74767250 & 718 \\ \end{tabular}\end{threeparttable}$

$\begin{threeparttable} \begin{tabular}{lD{.}{.}{10}D{.}{.}{10}D{.}{.}{3}} \multi... ..._{1.9}$} & 7.86148724 & 14.91398724 & 1.11 \\ \end{tabular}\end{threeparttable}$

( Question: why are the CPU times so different from those in 2000-02-02?)

$E_{V_O^{\cdot \cdot }}$ values should be the same as 2000-02-02; hence:

$\begin{threeparttable} \begin{tabular}{lD{.}{.}{10}D{.}{.}{10}D{.}{.}{10}} \mult... ...} & 14.91398724 & 15.02263140 & 3.03534308 \\ \end{tabular}\end{threeparttable}$

$\begin{center}\vbox{\input{2000-02-23-01.pslatex} }\end{center}$

The trend is not changed with respect to 2000-02-02.

Geometry of the optimized defect

Differently from 2000-02-02, where the starting and optimized orientations are coincident, in this case the relaxed orientation is along the direction, i.e. along the body diagonal of the cube defined by the eight oxygen ions inside the unit cell.

The following table shows the angle $\theta$ between the $\xy* {O};p+/r2em/*{H}**\dir{-}?>*\dir{>}\endxy$ vector and the direction, and the $\xy*{O};p+/r2em/*{H}**\dir{-}\endxy$ bond length:

$\begin{threeparttable} \begin{tabular}{lllll} \multicolumn{1}{c}{Oxide} &\multic... ...0433,1.430389 & 1.987786,1.987786,1.987877 \\ \end{tabular}\end{threeparttable}$

$\begin{threeparttable} \begin{tabular}{lll} \multicolumn{1}{c}{Oxide} &\multicol... ...b_{0.2}O_{1.9}$} & 0.00654176 & 0.96544166 \\ \end{tabular}\end{threeparttable}$

Representative input file


opti conp defect regi_before nodsymmetry
#conp defect single
dump every 1 la-OH.dump
maxcyc  200
cutb 3.0 # what does this mean? Ronny uses it.
title
Lanthanum solid solution
N.Sakai et al. Solid State Ionics 125(1999)325-331
end
cell
   5.490000 5.490000 5.490000  90.000000  90.000000  90.000000

size        9.88578122         20.00
centre      0.25   0.25   0.25
impurity     O2 core   0.25   0.25   0.25
interstitial H2 core   0.37354608 0.37354608 0.25000000
fractional   
############
# Cores
############
Ce4  core  0.000000   0.000000   0.000000  -3.700000 0.8
La   core  0.000000   0.000000   0.000000   3.00     0.2
O1   core  0.250000   0.250000   0.250000   0.07700  0.95
############
# Shells
############
Ce4  shel  0.000000   0.000000   0.000000   7.700000 0.8
O1   shel  0.250000   0.250000   0.250000  -2.07700  0.95
space
225

#########################
# 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
buck                                                    
Ce3 shel O1 shel    1731.61808  0.36372    14.43256  0.0 15.000
buck                                                    
La  core O1 shel    1439.7      0.36510     0.00000  0.0 15.000
buck                                                    
O1  shel O1 shel   22764.300000 0.149000   27.89000  0.0 15.000
buck                                                    
O2  core O1 shel   22764.300000 0.149000   27.89000  0.0 15.000
buck                                                    
H2  core O1 shel     311.970    0.35        0.0      0.0 15.000
morse
H2  core O2 core       7.05250  2.19860     0.9485   1.0 0.0 2.0
buck 
Ce4 shel O2 core    1986.830000 0.351070   20.40000  0.0 15.000
buck                                                    
La  core O2 core    1439.7      0.36510     0.00000  0.0 15.000
#########################
# Spring parameters
#########################
spring 
Ce4    291.750000
spring 
Ce3    291.750000
spring 
O1      27.29