Restart the DOS or band structure with BAND
*******************************************

BAND DOS Electronic band structure

It is quite likely that you did a calculation, but forgot to request
the DOS or BandStructure. Or maybe you did but want to use different
settings.

Fortunately it is possible to calculate these directly from the
previous calculation.

With the restart of the DOS it is possible to calculate the DOS with a
finer k-space sampling. In this example we first show an example where
the DOS does not match the band structure. This missing DOS problem
can be solved by simply using a better k-grid. However, it can also be
solved by doing a restart, using only a better k-grid for the DOS
calculation.


Step 1: Load the geometry
=========================

The have the geometry stored as an xyz file

   Download "Mo3WSeS7.xyz"

Let us load it into **AMSinput**.

   Start AMSinput
   **File → Import Coordinates...**
   Select the downloaded file "Mo3WSeS7.xyz" and click "OK"

The structure is a MoS2 slab with some substitutions

   [image]


Step 2: Calculation
===================

With the system loaded it is time to setup the calculation

   In the **Main** panel:
   Tick "Yes" next to **Calculate PDOS** and **Calculate band structure**

   [image]

   **File → Save As...**
   Save e.g. under "test_k=normal.ams"

Now run the calculation with **File → Run**.  This calculation may
take a few minutes.


Step 3: Inspecting the results
==============================

After the calculation is complete, open the results with **SCM → Band
Structure**. To highlight the missing DOS problem change the y-range
to -8 to -4 eV

   Double click on the "DOS/eV" axis of the DOS plot
   Set the range from 0 to 50

   [image]

   Double click on the "Energy (eV)" axis of the DOS plot
   Set the range from -8 to -4

   [image]

Now we can see the problem: there clearly is a band between -5.6 and
-5.2 eV, but the DOS is zero in this range.

   [image]


Step 4: The simple solution: more k-points
==========================================

The simple solution is to do the whole calculation with a better
k-grid.

   [image]

   In AMSinput, set the k-space quality to good (as shown above)
   **File → Save As...**
   Save e.g. under "test_k=good.ams"

Run the calculation with **File → Run**, and this calculation will
take a bit longer than before.

   Open with amsbands
   Modify the DOS plot axes as before

and now there is no longer DOS missing in the -5.6 and -5.2 energy
range.

   [image]


Step 5: Restarting the DOS with more k-points
=============================================

   Open "test_k=good.ams"
   Go to the **Details → Restart Details** panel and check DOS and band structure
   Select the file to restart from "test_k=normal.results/band.rkf"

   [image]

   **File → Save As...**
   Save e.g. under "test_k=normal_krestart=good"
   Run the calculation
   After the calculation is finished open it with amsbands
   Change the x-range to 0,50 and the y-range to -8,-4

The band structure and DOS look very similar to what we had with a
good k-grid for the whole calculation (see Step 4), but obtained in a
faster way, avoiding the need to do a full SCF with the good k-grid.
Note that there is no longer missing dos between -5.6 and -5.2 eV.

   [image]


Step 6: Refining the plot
=========================

In the final step we use more energy points for the dos grid and finer
sampling of the band structure

   Open "test_k=normal_krestart=good.ams"
   Go to **Properties → DOS** panel and change the energy interval (delta E) to 0.001

   [image]

   Go to **Properties → Band structure** panel and change the interpolation delta-K to 0.03
   Save as "test_k=normal.krestart=good_refined"

   [image]

The refined plot is

   [image]

The reference result obtained by simply doing a full SCF with good
k-grid and refined DOS DeltaE and BandStructure delta-K is

   [image]

and the results look very similar, so you do not need to perform this
calculation.
