Dear Dr. Dahal,
-> The comments of the referee suggest that the current manuscript on its
-> own does not meet our acceptance criteria. We feel that it will be in
-> your interest to combine your earlier submission BA11443 with the
-> current manuscript. We look forward to receiving such a modified
-> manuscript.
-
-BA11443 (Ref. 60) is a self contained and comprehensive manuscript,
-which already now has an appreciable length. Although dealing with the
-same material the present manuscript uses a different, continuative
-approach.
-
-While manuscript BA11443 constitutes a study on defects in
-carbon-implanted silicon exclusively investigated by first-principles
-methods, the present study picks up the limitation of the employed
-classical potential as revealed already in Ref. 42, investigates this
-limitation in more detail and proposes an approach to work around it
-enabling the application to classical potential molecular dynamics
-simulations. Although conclusions on the SiC precipitation in Si are
-already derived in manuscript BA11443, the present study is considered
-an interesting and self contained continuation since it allows for the
-description of larger systems and time scales than accessible by ab
-inito methods. Furthermore, a majority of the results of the classical
-potential as well as the ab initio results on defect structures are
-not presented in either of the two preceding publications.
-
-We would greatly appreciate if you could reconsider your decission and
-we look forward to receiving further comments. It would also be nice
-to know how the processing of manuscript BA11443 is now influenced by
-the present decission.
-
-Please find attached a reply to the comments of the referee, which we
-hope will clarify all your and the referee's concerns enabling a
-separated publication in the Physical Review B.
-
+Thank you very much for informing us about the status of our
+manuscript.
+
+The referee
+
+ i) requests a clarification of the relation of the present
+ manuscript to a previous submission of ours (BA11443)
+ ii) has reservations about the methodology used in the present work
+iii) suggests to possibly combine some account of the present
+ work with the previous submission BA11443.
+
+What concerns (ii), the classical potential molecular dynamics used in
+the present work certainly has limitations. Precisely in order to
+quantify these limitations, a comparison is made with ab initio
+calculations as well as earlier first-principles work (BA11443).
+Despite the shortcomings of classical potential simulations, they
+nevertheless provide valuable insight in the physical mechanism of
+silicon carbide precipitation on length and time scales which are not
+accessible to more accurate ab initio techniques. A detailed response
+to the referee's concerns is given below.
+
+Concerning (i) and (iii), the ab initio work BA11443 is a
+self-contained and comprehensive manuscript, which already now has an
+appreciable length. It is a first-principles study on defects in
+carbon-implanted silicon. In contrast, the present study mainly
+applies classical potentials to model the SiC precipitation in Si on
+large time and length scales. While the material is the same, the
+methodologies applied and the questions addressed in the present work
+and in BA11443 largely differ. For this reason, and because both
+manuscripts already contain a substantial amount of information, we
+believe it is not in the interest of the readers to combine the two
+manuscripts. Perhaps it would be good idea to make BA11443 available
+to the referee of the present work?
+
+Please find below a reply to the comments of the referee, which we
+hope will satisfactorily answer his concerns on the suitability of our
+work for publication in the Physical Review B.
Sincerely,
> It follows on naturally from a previous paper on the carbon
> interstitial in silicon (their ref 42), but does not appear to be a
> "serial publication". However, it also refers to an (as yet)
-> unpublished study (ref 60) of the same topic as the present paper with
-> almost the same authors, using ab initio MD. Perhaps the authors could
-> comment on how these two papers differ, and whether ref 60 improves on
-> the results of the present paper in such a way that makes present
-> paper superfluous.
+> unpublished study (ref 60) of the same topic as the present paper
+> with almost the same authors, using ab initio MD. Perhaps the
+> authors could comment on how these two papers differ, and whether
+> ref 60 improves on the results of the present paper in such a way
+> that makes present paper superfluous.
Manuscript BA11443 (Ref. 60) entitled 'First-principles study of
defects in carbon-implanted silicon' investigates single native and C
-point defects as well as their combinations in Si by highly accurate
-ab initio methods. In that, it constitutes a self contained,
-substantial study.
-
-The present work studies in more detail the limitation of the employed
-classical potential by comparing it to the results of ab initio
-calculations. We would like to point out that a majority of the
-results of the ab initio as well as the classical potential
-investigations on defect structures, which are in the closer context
-of this manuscript, have not been presented in either of the two
-preceding documents.
-Additionally, a work around is proposed to overcome the limitation of
-the potential as well as the general problem inherent to MD describing
-phase transitions made up of a multiple of infrequent transition
-events. This enables the observation of a phase transition of the
-obtained structure with increasing temperature during C insertion.
-
-Although conclusions on the SiC precipitation in Si are already
-derived from the DFT study on single defects and some selected
-combinations, the classical potential MD simulations allow the
-investigation of larger and, thus, much more complex systems on a
-larger time scale, reinforcing conclusions concerning the SiC
-precipitation in Si.
-
-There are no contradictions or improvements to the current study in
-Ref. 60 that would make one of the manuscripts obsolteted by the
-other.
-
-Both manuscripts constitute self contained and comprehensive studies,
-which - in our opinion - should be presented separately.
+point defects as well as their combinations in Si exclusively by first
+principles calculations. In that, it constitutes a self-contained,
+rather substantial study.
+
+The present work studies the limitations of classical potentials by
+means of comparison with first-principles results (and has virtually
+no overlap with the results of BA11443). Based on this comparison, an
+approach is proposed that allows to overcome some of the limitations
+of the classical potentials as well as the general problem inherent to
+MD describing phase transitions made up of a multiple of infrequent
+transition events. This enables us to simulate the phase transition of
+the Si structure during C insertion.
+
+Although conclusions on the SiC precipitation in Si were already
+derived in the DFT study BA11443 based on calculatiuons for single
+defects and some selected combinations, the classical potential MD
+simulations allow the investigation of far larger and, thus, much more
+complex systems on a larger time scale, reinforcing conclusions
+concerning the SiC precipitation in Si.
+
+There are no contradictions or improvements to the present study in
+BA11443 that would make either manuscript obsolete.
> I have some serious reservations about the methodology employed in
> this paper, for reasons that are discussed at length in it. 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. Actually, the
-> proof I would need is probably within the simulations of ref 60, hence
-> my question above! The problems I refer to are 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,
-> probably due to the short cut-off of the interactions. 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 over-estimated by a similar
-> factor, which is demonstrably untrue in this case, where the C_s
-> formation energy is actually underestimated. There are long
-> discussions of these points in the paper, which leads me to the
+> the method do not introduce further uncertainties, and I would need
+> a bit more convincing that the results are actually valid. Actually,
+> the proof I would need is probably within the simulations of ref 60,
+> hence my question above! The problems I refer to are 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, probably due to the short cut-off of the interactions.
+> 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 over-estimated
+> by a similar factor, which is demonstrably untrue in this case,
+> where the C_s formation energy is actually underestimated. There are
+> long discussions of these points in the paper, which leads me to the
> conclusion that the EA potential used is unreliable in these
> simulations, possibly unless backed up by some ab initio work, which
> the authors have done in ref 60.
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
+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 'accomodated' within this short
+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
the respective formation energies are quite well described, too (at
least they are not necessarily overestimated in the same way).
-While the properties of some structures near the equilibirum position
-are well described the above mentioned effects increase for
-structures/dynamics more distant from the balanced state. Thus, for
-instance, it is not surprising that short range potentials show
-overestimated melting temperatures. This is not only true for the EA
-but also (even to a greater extent) for the Tersoff potential, one of
-the most widely used classical potentials for the Si/C system. The
-fact that the melting temperature is drastically overestimated
-although the cohesive energies are nicely reproduced indicates that
-there is no reason why the cohesive and formational energies should be
-overestimated to the same extend in order to legitimate the increase
-in temperature to appropriately consider the overestimated barrier
-heights for diffusion.
+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
+surprising that short range potentials show overestimated melting
+temperatures. This is not only true for the EA but also (to an even
+larger extent) for Tersoff potentials, one of the most widely used
+classical potentials for the Si/C system. The fact that the melting
+temperature is drastically overestimated although the cohesive
+energies are nicely reproduced indicates that there is no reason why
+the cohesive and formational energies should be overestimated to the
+same extent in order to legitimate the increase in temperature to
+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.
+observed, which can be very well explained and correlated to
+experimental findings.
The underestimated energy of formation of substitutional C for the EA
-potential turns out to not constitute a real problem concerning the
-raised question (interstitial versus substitutional C). Since we deal
-with a perfect Si crystal and conservation of particles 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 inito calculations.
-
-> Therefore, I do not feel that this paper can stand alone - either its
-> conclusions are contradicted by those of ref 60 (in which case there's
-> no need to publish this paper), or supported by them (in which case
-> ref 60 supercedes this paper, and some brief account of this work
-> could be included in it).
+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)
+
+> Therefore, I do not feel that this paper can stand alone - either
+> its conclusions are contradicted by those of ref 60 (in which case
+> there's no need to publish this paper), or supported by them (in
+> which case ref 60 supercedes this paper, and some brief account of
+> this work could be included in it).
As mentioned above, there are no conclusions in Ref. 60 that
-contradict to the results of the present manuscript. Indeed, results
-of Ref. 60 are important for the current study and, therefore,
-supporting this work. However, the different approach, i.e. modelling
+contradict to the results of the present manuscript. Indeed, the
+results of Ref. 60 are important for the present study and, therefore,
+supporting this work. However, the different approaches, i.e. modeling
thousands of C atoms incorporated into a large Si host matrix by
-molecular dynamics simulations on a large time scale opposed to highly
-accurate investigations of the structure of single and double defects
-in Si and some selected diffusion processes, militates the separate
-publication of the results presented in the two manuscripts.
+molecular dynamics simulations on a large time scale vs accurate
+investigations of the structure of single and double defects in Si and
+some selected diffusion processes, suggests the separate publication
+of the results.
+
+
+
+Summary of changes
+------------------
+
+ - = line removed
+ + = line added
+
+Change 1
+--------
+
++
++Thus, the underestimated energy of formation of C$_{\text{s}}$ within
+ the EA calculation does not pose a serious limitation in the present
+ context.
+
++Since C is introduced into a perfect Si crystal and the number of
+ particles is conserved in simulation, the creation of C$_{\text{s}}$
+ is accompanied by the creation of Si$_{\text{i}}$, which is
+ energetically less favorable than the ground state, i.e. the
+ C$_{\text{i}}$ \hkl<1 0 0> DB configuration, for both, the EA and ab
+ initio treatment.
+
+Change 2
+--------
+
+-The cut-off function of the short range potential limits the
+ interaction to nearest neighbors, which results in overestimated and
+ unphysical high forces between neighbored atoms.
+
++The cut-off function of the short range potential limits the
+ interaction to nearest neighbors.
+
++Since the total binding energy is, thus, 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.
-If considered helpful, we would be happy to send a copy of manuscript
-BA11443 to the referee.
++While cohesive and formational energies are often well described,
+ these effects increase for non-equilibrium structures and dynamics.
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