From: hackbard Date: Fri, 15 Apr 2011 09:31:41 +0000 (+0200) Subject: added reply 01 of sic prec X-Git-Url: https://hackdaworld.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c8b7b3b5a4d4c04973294dfc9f85cf5d56a9f624;p=lectures%2Flatex.git added reply 01 of sic prec --- diff --git a/posic/publications/sic_prec_reply01.txt b/posic/publications/sic_prec_reply01.txt new file mode 100644 index 0000000..4f08e43 --- /dev/null +++ b/posic/publications/sic_prec_reply01.txt @@ -0,0 +1,180 @@ + +Re: BC11912 + Combined ab initio and classical potential simulation study on the + silicon carbide precipitation in silicon + by F. Zirkelbach, B. Stritzker, K. Nordlund, et al. + + +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. + + +Sincerely, + +Frank Zirkelbach + + + +Response to the comments of the referee +--------------------------------------- + +> 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. + +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. + +> 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 +> 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 +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 +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. (Phys. Rev. B 76, 224103 (2007)). + +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). + +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. + +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 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). + +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 +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. + +If considered helpful, we would be happy to send a copy of manuscript +BA11443 to the referee. +