Simulation of STM Pictures

To generate a STM image of a surface, two calculations need to be done, both using the same geometry, preferrentially a surface slab.

A: Single point calculation of the structure of interest. Both a CHGCAR and a WAVECAR file need to be obtained. For this, activate the printout of both files:

• LCHARG = .TRUE. Activate printout of CHGCAR.
• LWAVE = .TRUE. Activate printout of WAVECAR.

B: Calculate the partial charge density which serves as template for simulating the STM picture. Copy the calculated CHGCAR and WAVECAR files to the folder and add the following keywords to the INCAR file:

• LPARD = .TRUE: Evaluate partial charge density.
• ISTART = 1 Read in the existent WAVECAR file.
• NBMOD = -3 Calculate partial charge density in an energy range given by EINT.
• EINT = [value1] [value2] The energy range for the partial charge density. Usually, [value1] should be set to the negative of the reported experimental STM current to compare with (e.g., -1 for 1 eV current), [value2] should be zero.

The second calculation is only an evaluation of the pre-calculated WAVECAR and should be done within some second to minutes. After this, the PARCHG file can be opened with p4v together with the vasprun.xml file. In p4v, go to the STM mode, switch to constant current mode and align the Isos. density until a nice picture can be seen (usual values: 0.01 to 0.03). Click on the camera symbol on the left to make a screenshot.

Much more convenient, however, is our new eval_stm program, which enables the calculation of STM images including axis descriptions. See in the respective wiki page for more details.