> response to all recommendations and criticisms.
We decided to follow yours and the referee's suggestion to merge the
-two manuscripts into a single comprehensive manuscript.
+two manuscripts in a single comprehensive manuscript.
Please find below the summary of changes and a detailed response to
the recommendations of the referee.
--------------- Response to recommendations ----------------
-TODO: add changes applied due to criticism ...
-
> I am not happy with these two papers for a multitude of reasons,
> and I recommend that the authors rewrite them as a single longer
> paper, to eliminate the criticism of serial publication. I do not
other ab initio studies. However, the observed differences in energy
within our systematic DFT study are considered reliable.
-> 2. Why is 216 atoms a large enough supercell many defect
+> 2. Why is 216 atoms a large enough supercell - many defect
> properties are known to converge very slowly with supercell size.
Of course, choosing a supercell containing 216 atoms constitutes a
> are seen for constant volume calculations (on a few simple
> examples, say)?
-In experiment substrate swelling is observed for high-dose carbon
-implantation into silicon. Indeed, using the NpT ensemble for
-calculations of a single (double) C defect in Si is questionable.
-However, only small changes in volume were observed and, thus, it is
-assumed that there is no fundamental difference between calculations
-in the canonical and isothermal-isobaric ensemble.
+Differences are supposed to be negligible small since only small
+changes in volume are detected. However, in experiment, substrate
+swelling is observed. Thus, to allow for full relaxation, simulations
+were performed in the NpT ensemble. However, for the above-mentioned
+reason, no fundamental differences are expected for single defect
+configurations in the canonical and isothermal-isobaric ensemble with
+respect to energy.
+
+A respective statement was added to the methodology section.
> 4. What method do they use to determine migration paths? How can
> they convince us that the calculations cover all possible
> number of methods used in the literature to address it are the
> authors aware of them? Have they used one of them?
-A slightly modified version of the constrained conjugate gradient
-relaxation method is used. It is named in the very beginning of the
-second part of chapter II and a reference is given. Although, in
-general, the method not necessarily unveils the lowest energy
-migration path it gives reasonable results for the specific system.
-This can be seen for the resulting pathway of C interstitial DB
-migration, for which the activation energy perfectly matches
-experimental data.
-
-For clarity we added a statement, however, that of course the true
-minimum energy path may still be missed. (-> Change 4)
+The constrained relaxation technique is used to determine migration
+pathways. The method is named and a reference is given in the
+methodology section. The method not necessarily unveils the lowest
+energy migration path. The supposed saddle point structure needs to be
+attested by investigating the vibrational modes. However, reasonable
+results are obtained for the specific system. In fact, so far, the
+best quantitative agreement with experimental findings has been
+achieved concerning the interstitial carbon mobility (PRB 82, 094110
+(2010)) utilizing the constrained relaxation technique. Thus, obtained
+migration paths are assumed to be valid without investigating the
+vibrational modes of every single supposed saddle point configuration.
+
+For clarity we added a statement that, of course, the true minimum
+energy path may still be missed.
> 5. I have some serious reservations about the methodology
> employed in the MD calculations. The values given for the basic
> stabilities and migration energies in some cases disagree
> radically with those calculated by VASP, which I would argue
> (despite 4 above) to be the more reliable values. The main
+
+Indeed, discrepancies exist. However, both methods predict the C-Si
+100 DB configuration to be the ground-state structure. The
+underestimated energy of formation of substitutional C for the EA
+potential does not pose a problem in the present context. Since we
+deal with a perfect Si crystal and the number of particles is
+conserved, the creation of substitutional C is accompanied by the
+creation of a Si interstitial. The formation energies of the different
+structures of an additional C atom incorporated into otherwise perfect
+Si shows the same ground state, i.e. the C-Si 100 DB structure, for
+classical potential as well as ab initio calculations.
+
+This is discussed in full detail in section V in the combined
+manuscript.
+
> problems is the huge over-estimate of the C interstitial
> migration energy (a process which is at the heart of the
> simulations) using the potential used in the paper. I am not
> convinced that the measures they take to circumvent the problems
> in the method do not introduce further uncertainties, and I would
> need a bit more convincing that the results are actually valid.
+
+We hope to be able to convince by responding to the following
+statement of the referee.
+
> The authors' circumvention of this is to do the simulations at
> much heightened temperatures. However, this only gives a good
> model of the system if all cohesive and migration energies are
> need a critical scrutiny, which I am not very convinced by in
> this case.
-TODO: add idea that elevated temperatures are considered necessary to
-deviate the system out of equilibrium, as assumed to be the case in IBS
-
-you can always add constant to energy.
-formation energies are not overestimated
-just the migration barriers are
-to increase probability of transitions, temperature is increased
-occupation of energetically more unfavorable states likewise increased
-indeed, sub conf, which is slightly higher than c-si DB, is increased
-comparing with experimental findings that suggest c sub for higher
-temperatures gives rise to the conclusion that the increased
-temperatures are needed to deviate the system out of the ground state!
-
-There is not necessarily a correlation of cohesive energies or defect
-formation energies with activation energies for migration. Cohesive
-energies are most often well described by the classical potentials
-since these are most often used to fit the potential parameters. The
-overestimated barriers, however, are due to the short range character
-of these potentials, which drop the interaction to zero within the
-first and next neighbor distance using a special cut-off function.
-Since the total binding energy is 'accommodated' within this short
-distance, which according to the universal energy relation would
-usually correspond to a much larger distance, unphysical high forces
-between two neighbored atoms arise. This is explained in detail in the
-study of Mattoni et. al. (PRB 76, 224103 (2007)).
+There is not necessarily a correlation of the cohesive and migration
+energies. You can always add a constant to the cohesive energies of
+respective structures. It is the difference in the cohesive energies
+of structures within the migration path, which determines the
+migration barrier.
+
+In fact, cohesive energies are most often well described by the
+classical potentials since these are most often used to fit the
+potential parameters.
+
+The overestimated migration barrier, however, is due to the short
+range character of the potential, which drops the interaction to
+zero within the first and next neighbor distance using a special
+cut-off function as explained in PRB 76, 224103 (2007). The
+overestimated barrier and slightly different pathway (however,
+starting and final configuration/orientation agree) is indeed
+demonstrated for the carbon interstitial within the present study.
+Since the reason of overestimation is inherent to the short range
+potential, migration pathways among other configurations are
+likewise overestimated.
Since most of the defect structures show atomic distances below the
critical distance, for which the cut-off function is taking effect,
the respective formation energies are quite well described, too (at
least they are not necessarily overestimated in the same way).
+Thus, increased temperatures result in an increased probability of
+transition. Obviously, this enables the structural transformation
+into energetically less stable structures of substitutional carbon and
+interstitial silicon that are observed in the high temperature
+simulations. Being in nice agreement with experimental findings, these
+results suggest the usage of increased temperatures to constitute a
+necessary condition to deviate the system out of the ground state as
+it is the case in the ion beam synthesis process.
+
+A respective statement and a more detailed comparison with experiment
+was added to the combined version of the manuscript.
+
+Again, we would like to repeat the arguments that legitimate the usage
+of increased temperatures although cohesive and formational energies
+are not ovrestimated in the same way than the migration barriers.
While the properties of some structures near the equilibrium position
are well described, the above mentioned effects increase for
non-equilibrium structures and dynamics. Thus, for instance, it is not
appropriately consider the overestimated barrier heights for
diffusion.
-Indeed, a structural transformation with increasing temperature is
-observed, which can be very well explained and correlated to
-experimental findings.
-
-The underestimated energy of formation of substitutional C for the EA
-potential does not pose a problem in the present context. Since we
-deal with a perfect Si crystal and the number of particles is
-conserved, the creation of substitutional C is accompanied by the
-creation of a Si interstitial. The formation energies of the
-different structures of an additional C atom incorporated into
-otherwise perfect Si shows the same ground state, i.e. the C-Si 100 DB
-structure, for classical potential as well as ab initio calculations.
-
-The arguments discussed above are now explained in more detail in the
-revised version of our work. (-> Change 1, Change 2)
-
+Indeed the cut-off effect increases if the system is deviated from
+equilibrium. Thus, to mimic IBS, a process far from equilibrium,
+increased temperatures are exceptionally necessary if short range
+potentials are utilized.
--------------- Summary of changes ----------------
-
projects / lectures / latex.git / blobdiff