From: hackbard Date: Fri, 16 Apr 2010 14:51:49 +0000 (+0200) Subject: little more on increased temperatures, quality value defned X-Git-Url: https://hackdaworld.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=742d9867fd5f4cfb04d5aba6f59bbdf3cbd00eb8;p=lectures%2Flatex.git little more on increased temperatures, quality value defned --- diff --git a/posic/thesis/md.tex b/posic/thesis/md.tex index 2318a65..a51304e 100644 --- a/posic/thesis/md.tex +++ b/posic/thesis/md.tex @@ -264,13 +264,21 @@ Due to the limitations of short range potentials and conventional MD as discusse The simulation sequence and other parameters aside system temperature remain unchanged as in section \ref{subsection:initial_sims}. Since there is no significant difference among the $V_2$ and $V_3$ simulations only the $V_1$ and $V_2$ simulations are carried on and refered to as low carbon and high carbon concentration simulations. Temperatures ranging from $450\,^{\circ}\mathrm{C}$ up to $2050\,^{\circ}\mathrm{C}$ are used. -A quality value $Q$ is introduced, which is defined as +A simple quality value $Q$ is introduced, which helps to estimate the progress of structural evolution. +In bulk 3C-SiC every C atom has four next neighboured Si atoms and every Si atom four next neighboured C atoms. +The quality could be determined by counting the amount of atoms which form bonds to four atoms of the other species. +However, the aim of the simulation on hand is to reproduce the formation of a 3C-SiC precipitate embedded in c-Si. +The amount of Si atoms and, thus, the amount of Si atoms remaining in the silicon diamond lattice is much higher than the amount of inserted C atoms. +Thus, counting the atoms, which exhibit proper coordination is limited to the C atoms. +The quality value is defined to be \begin{equation} Q = \frac{\text{Amount of C atoms with 4 next neighboured Si atoms}} {\text{Total amount of C atoms}} \text{ .} \label{eq:md:qdef} \end{equation} -In 3C-SiC every C atom has four next neighboured Si atoms resulting in $Q=1$. +By this, bulk 3C-SiC will still result in $Q=1$ and precipitates will also reach values close to one. +However, since the quality value does not account for bond lengthes, bond angles, crystallinity or the stacking sequence high values of $Q$ not necessarily correspond to structures close to 3C-SiC. +Structures that look promising due to high quality values need to be further investigated by other means. Figure ... shows the radial distribution of Si-C bonds and the corresponding quality paragraphs.