DFT + Hubbard U, PDOS

This tutorial will show you how to perform a single point calculation with the DFT+U formalism using the BAND engine.

Step 1: amsinput

1. Start AMSinput
2. Switch to BAND: ADFPanel → BANDPanel
/scm-uploads/doc.2022/Tutorials/_images/amsinput_BAND_Main.png

Step 2: Setup the system - NiO

You can copy-paste the following information into the AMSinput directly.

2

Ni    0.000  0.000  0.000
O     2.085  2.085  2.085
VEC1  0.000  2.085  2.085
VEC2  2.085  0.000  2.085
VEC3  2.085  2.085  0.000

By default, only the central unit cell is shown. To see a few unit-cell repetitions:

Click on View → Periodic → Repeat Unit Cells

Step 3: BP86 without Hubbard

Change the calculation setup (Unrestricted, XC functional, basis set) as follows:

1. Check the Unrestricted box.
2. Set XC functional to GGA:BP86.
3. Set Basis Set to TZP
4. Tick the checkbox DOS
/scm-uploads/doc.2022/Tutorials/_images/Hubbard_2.png

Step 3a: Run the calculation

Now you can save and run the calculation.

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

Step 3b: Checking the results

After the calculation finished, you can check the Output for the ‘Band Gap Info’.

SCM → Output
Properties → Band Gap Info

One can see that there is no band gap at all. This contradicts experimental studies, which predict values between 3.7 to 4.3 eV.

/scm-uploads/doc.2022/Tutorials/_images/BP_Output_BandGapInfo.png

Plotting and examining the partial density of states (pDOS) for this calculation reveals that the d-orbital contributions of Ni are crossing the Fermi level.

SCM → DOS
Select the Ni atom.
Choose Partial → Ni(1) → D-DOS
/scm-uploads/doc.2022/Tutorials/_images/Ni_D_DOS_BP.png

Step 4: Run the calculation - BP86+U

Go back to the Main menu of amsinput, change to HubbardU menu, and apply an U value of 0.6 a.u. to the d-orbitals of the Ni atom.

Go to Model → HubbardU.
Set for Ni the l-value to d and the U value to 0.6.
/scm-uploads/doc.2022/Tutorials/_images/Hubbard_4.png

This will influence the Hamiltonian and results in a state which tries to omit partial occupation or degeneracy w.r.t. the d-orbitals.

Step 4a: Run the calculation

Now you can save and run the calculation.

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

Step 4b: Checking the results

After the calculation finished, you can check the Output for the ‘Band Gap Info’.

SCM → Output
Properties → Band Gap Info

One can see that there is now a band gap of around 2 eV. This is still less than the experimental values. That can be traced back to the neglection of the correct magnetic behavior of NiO.

/scm-uploads/doc.2022/Tutorials/_images/BP+U_Output_BandGapInfo.png

Plotting and examining the partial density of states (pDOS) for this calculation reveals that the d-orbital contributions of Ni are no longer crossing the Fermi level.

SCM → DOS
Select the Ni atom.
Choose Partial → Ni(1) → D-DOS
/scm-uploads/doc.2022/Tutorials/_images/Ni_D_DOS_BP+U.png