PEDA-NOCV - decomposing the orbital relaxation term
***************************************************

BAND Bonding Analysis Energy Decomposition Analysis

This tutorial will teach you how to perform a Periodic Energy
Decomposition Analysis (PEDA) combined with the Natural Orbitals for
Chemical Valency (NOCV) method for periodic systems with BAND. It will
also show how to visualize NOCV orbitals and NOCV deformation
densities.


Setting up the System and the Calculation
=========================================

   Follow the instructions in the sections "Set up the system" and "Set up the PEDA calculation" of the first PEDA Tutorial.


Preparations for the PEDA-NOCV calculation
------------------------------------------

Now the PEDA-NOCV has to be switched on. Go to the PEDA-NOCV menu,

   Panel bar **Properties → PEDA-NOCV**
   Check the **Perform PEDA-NOCV analysis** checkbox

You can define a NOCV eigenvalue threshold (default: 0.001) which
handles the amount of output.

[image]

Keep in mind that the PEDA-NOCV is implemented for \Gamma-only
systems. So, go to the 'Integration K-Space' menu,

   Panel bar **Details → K-Space Integration**
   Set the 'K-Space' to 'Gamma only'

   [image]


Save and run the calculation
----------------------------

Now you can save and run the calculation.

   **File → Save**, give it a name and press Save.
   **File → Run**


Step 2: Checking the results
============================

After the calculation of the fragments and the PEDA are finished you
can look for the PEDA results. Therefore, open the "Output" using the
SCM dropdown menu.

   **SCM → Output**

You can jump to the 'PEDA-NOCV Energy Terms' via the corresponding
button in the 'Properties' drop-down menu.

   **Properties → PEDA-NOCV Energy Terms**

Reference results:

[image]


Step 3: Plotting NOCV orbitals and deformation densities
========================================================

You can visualize the charge NOCV deformation densities which describe
the charge flow between the fragments. Therefore, open the "View"
using the SCM drop-down menu.

   **SCM → View**
   Press CTRL+2 to view along the Y-axis
   **Fields → Grid → Medium**

Depending on your preferences (w.r.t. showing atoms of neighboring
cells) you will end up with the following representation of AMSview.

[image]


Step 3a: Plotting NOCV deformation densities
--------------------------------------------

We will now visualize some NOCV deformation densities

   [image: AddButton][image] **→ Isosurface: With Phase**
   Click on **Select Field → NOCV Def Densities...**

A table will appear which will let you select the NOCV deformation
density.

   Click on the first entry in the table to visualize the first NOCV deformation density
   Set the isovalue to **0.000025**
 [image]

According to the information in the "NOCV Def Densities" table, the
first NOCV deformation density is a combination of NOCV orbital 1 (the
first term denotes the donor/occupied NOCV) and 150 (the second term
denotes the acceptor/unoccupied NOCV). This deformation density
visualizes the charge flow from red to blue lobes. Here, the charge
transfer from the CO to the MgO surface is shown.

You can toggle extra visualization options by clicking on the tiny
arrow next to "Isosurface: With Phase":

[image]


Step 3b: Plotting NOCV orbitals
-------------------------------

These NOCV orbitals can be visualized by changing the field to 'NOCV
Orbitals'.

   Click on the **field selector → NOCV Orbitals**

Selecting the 1st and 150th NOCV orbitals will trigger the calculation
of their isosurfaces. The orbitals can then be visualized one at a
time. (Or you can add a second isosurface to show both of them.)

NOCV orbital 1 shows predominantly a lone-pair localized at the CO
fragment (note: the iso value is set to 0.01)

[image]

NOCV orbital 150 shows predominantly a lobe connecting the CO fragment
with a Mg atom of the surface.

[image]
