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--- exercises:2016_uzh_cmest:defects_in_graphene [2016/11/14 08:28] – tmueller
+++ exercises:2016_uzh_cmest:defects_in_graphene [2020/08/21 10:15] (current) – external edit 127.0.0.1
@@ Line 18: / Line 18: @@
 Quick question: Does it matter which carbon atom you remove? (hint: what kind of boundary conditions do we impose?)
-Calculate the energy of the vacancy formation, that is $E_v = E_2 (N-1)/N \cdot E_1$ where $E_1$ is the energy of the complete system, $E_2$ that of the system with a vacancy and $N$ the number of atoms.
+Calculate the energy of the vacancy formation, that is $E_v = E_2 - \frac{N-1}{N} \cdot E_1$ where $E_1$ is the energy of the complete system, $E_2$ that of the system with a vacancy and $N$ the number of atoms.
 ===== Analyze the PDOS =====
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 Now we are going to investigate the effect an adsorbent has on graphene.
-====== Change in energy ======
+===== Change in energy =====
@@ Line 48: / Line 48: @@
 Try to explain based on the lecture what might be the problem.</note>
-====== Displacements ======
+===== Displacements =====
+We are furthermore interested in the change of structure this adsorbent causes. Try to visualize which atoms have to assume a new position in order to minimize the total energy. That is: plot $\sqrt{(x^i-x^i_0)^2 + (y^i-y^i_0)^2 + (z^i-z^i_0)^2}$ in a sensible manner (one which also retains the geometry of graphene).
+======= Analyzing defects in hexagonal Boron-Nitride =======
+Repeat the calculations of the vacancy formation, defect formation and adsorption for the h-BN-layer structure, taking into account that now both the N and the B can be replaced.
+Compare the energies for the two cases, where is a vacancy more likely to be and on top of which atom does an oxygen atom preferably adsorb.
+<note tip>Use the total energy of a B or N atom when calculating the vacancy formation energy.</note>
+Since N and B are radicals, you have to include the following keywords/options in the right places (use the CP2K manual):
+  * ''UKS = .TRUE.''
+  * ''MULITPLCITY = ...''
-We are furthermore interested in the change of structure this adsorbent causes. Try to visualize which atoms have to adopt a new position in order to minimize the total energy. That is: plot $\sqrt{(x^i-x^i_0)^2 + (y^i-y^i_0)^2 + (z^i-z^i_0)^2}$ in a sensible manner (one which also retains the geometry of graphene).