# TD-CDFT Response properties for a 2D periodic system (NewResponse)¶

BAND can calculate response properties such as the frequency-dependent dielectric function within the theoretical framework of time-dependent current density function theory (TD-CDFT).

This introductory tutorial will show you how to:

Set up and run a

**BAND**single point calculation (using**AMSjobs**and**AMSinput**) for an MoS_{2}monolayerSet up and run a

**BAND**TD-CDFT, linear response calculation (using**AMSjobs**and**AMSinput**) with the`NewResponse`

method for an MoS_{2}monolayerVisualize the dielectric function using

**AMSspectra**

If you are not at all familiar with our Graphical User Interface (GUI), check out the Introductory tutorial first.

## Step 1: Create the system¶

We now want to **create a** MoS_{2} **monolayer**. Let us import the geometry from our database of structures

**AMSinput**.

**Crystals → MoS2_Monolayer**. (you have to click on the

**triangle**to the right of

**Crystals**to expand the list)

**View → Periodic → Periodic View Type → Repeat Unit Cell**

If you succeed, your GUI should resemble the following picture:

## Step 2: Run a Singlepoint Calculations (LDA)¶

To get an idea regarding the performance of the LDA XC functional for the MoS_{2} monolayer, we first run a single-point calculation with the aim of analyzing the resulting band structure. We will already chose the calculation settings to be the same as for the following linear-response calculation with TD-CDFT: e.g. the basis set, the numerical quality, use of symmetry and the sampling of k-space.

**Basis set**to

**DZP**

**Numerical Quality**to

**Basic**

**Calculate band structure**and

**Calculate DOS**check-boxes

**Details → K-Space Integration**and set

**Number of points**to ‘

**11 11**’.

**Details → Symmetry**and de-select the check box

**Use of symmetry**

Now, everything is prepared for the single-point calculation.

**File → Save As…**, use name LDA_SP.ams

**File → Run**

With the help of the bandstructure we can validate that basic electronic properties are reproduced by this k-space sampling using only LDA as XC functional. Unlike the multilayered MoS_{2}, which has an indirect band gap, the MoS_{2} monolayer has a direct band-gap. (see also Ref)

**SCM → Logfile**

**SCM → Band Structure**

## Step 3: Run an NewResponse Calculation (ALDA)¶

We can now start the calculation of the frequency-dependent, dielectric function using linear response TD-CDFT. As a reasonable frequency range we shall sample from 1.0 eV to 3.0 eV with a step size of 0.1 eV.

**Calculate band structure**and

**Calculate DOS**boxes.

**Properties → Dielectric Function (TD-CDFT)**.

**Method**to

**NewResponse**.

**Number of frequencies**to

**21**.

**Starting frequency**to

**1.0**.

**End frequency**to

**3.0**.

**Criterion**to

**0.1**.

**Components**.

Since we have already calculated the SCF results in the previous run, we can restart the SCF from the band.rkf file (this will save some time during the SCF procedure)

**Details → Restart Details**.

**LDA_SP.results**

**SCF**next to

**Restart**

Tip

This allows us to split the frequency range into smaller parts without too much of an overhead due to the SCF convergence for the ground state properties. One could even think about restarting from a hybrid DFT calculation with e.g. HSE06.

We are set to run the calculation now:

**File → Save As…**, use name ALDA_TDCDFT.ams

**File → Run**

After the calculation finished, we can analyze the calculated dielectric function by plotting it with **AMSspectra**.

**SCM → Spectra**

**Spectra → TD-CDFT → Dielectric Function → XX**(you can move the legend with the mouse by drag and drop it to the desired location)

With respect to the accuracy of our calculation we can reproduce the main features of the dielectric function for this system. We cannot expect the spin-orbit splitting of the first transition at around 1.9 eV to 2.1 eV, since we don’t use **Spin-Orbit Relativistic ZORA**. Furthermore, the absolute values of the dielectric function depends on the assumed two-dimensional volume for the surface. Since this definition is arbitrary, we can change the value for the **Volume cutoff**, so that the static dielectric function is reproduced.