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Modified discussion of twobody symmetry

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git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@3958 f3b2605a-c512-4ea7-a41b-209d697bcdaa
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athomps
2010-04-06 15:10:15 +00:00
parent b12d4c13d1
commit 169ffd2711
2 changed files with 18 additions and 6 deletions
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10
doc/pair_tersoff.html
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@ -107,14 +107,20 @@ three-body parameters for SiCSi and SiSiC entries will not, in
general, be the same. The parameters used for the two-body general, be the same. The parameters used for the two-body
interaction come from the entry where the 2nd element is repeated. interaction come from the entry where the 2nd element is repeated.
Thus the two-body parameters for Si interacting with C, comes from the Thus the two-body parameters for Si interacting with C, comes from the
SiCC entry. By symmetry, the twobody parameters in the SiCC and CSiSi SiCC entry.
entries should thus be the same. The parameters used for a particular </P>
<P>The parameters used for a particular
three-body interaction come from the entry with the corresponding three-body interaction come from the entry with the corresponding
three elements. The parameters used only for two-body interactions three elements. The parameters used only for two-body interactions
(n, beta, lambda2, B, lambda1, and A) in entries whose 2nd and 3rd (n, beta, lambda2, B, lambda1, and A) in entries whose 2nd and 3rd
element are different (e.g. SiCSi) are not used for anything and can element are different (e.g. SiCSi) are not used for anything and can
be set to 0.0 if desired. be set to 0.0 if desired.
</P> </P>
<P>Note that the twobody parameters in entries such as SiCC and CSiSi
are often the same, due to the common use of symmetric mixing rules,
but this is not always the case. For example, the beta and n parameters in
Tersoff_2 <A HREF = "#Tersoff_2">(Tersoff_2)</A> are not symmetric.
</P>
<P>We chose the above form so as to enable users to define all commonly <P>We chose the above form so as to enable users to define all commonly
used variants of the Tersoff potential. In particular, our form used variants of the Tersoff potential. In particular, our form
reduces to the original Tersoff form when m = 3 and gamma = 1, while reduces to the original Tersoff form when m = 3 and gamma = 1, while

10
doc/pair_tersoff.txt
View File

@ -104,14 +104,20 @@ three-body parameters for SiCSi and SiSiC entries will not, in
general, be the same. The parameters used for the two-body general, be the same. The parameters used for the two-body
interaction come from the entry where the 2nd element is repeated. interaction come from the entry where the 2nd element is repeated.
Thus the two-body parameters for Si interacting with C, comes from the Thus the two-body parameters for Si interacting with C, comes from the
SiCC entry. By symmetry, the twobody parameters in the SiCC and CSiSi SiCC entry.
entries should thus be the same. The parameters used for a particular
The parameters used for a particular
three-body interaction come from the entry with the corresponding three-body interaction come from the entry with the corresponding
three elements. The parameters used only for two-body interactions three elements. The parameters used only for two-body interactions
(n, beta, lambda2, B, lambda1, and A) in entries whose 2nd and 3rd (n, beta, lambda2, B, lambda1, and A) in entries whose 2nd and 3rd
element are different (e.g. SiCSi) are not used for anything and can element are different (e.g. SiCSi) are not used for anything and can
be set to 0.0 if desired. be set to 0.0 if desired.
Note that the twobody parameters in entries such as SiCC and CSiSi
are often the same, due to the common use of symmetric mixing rules,
but this is not always the case. For example, the beta and n parameters in
Tersoff_2 "(Tersoff_2)"_#Tersoff_2 are not symmetric.
We chose the above form so as to enable users to define all commonly We chose the above form so as to enable users to define all commonly
used variants of the Tersoff potential. In particular, our form used variants of the Tersoff potential. In particular, our form
reduces to the original Tersoff form when m = 3 and gamma = 1, while reduces to the original Tersoff form when m = 3 and gamma = 1, while