Confusion while creating 2D surface slab from 3D bulk using SLABCUT keyword

R.Zosiamliana

Dear Crystal users and developers,

I am currently working in the investigation of 3D bulk to 2D surface slab properties.

I actually do not understand when we create 2D surface slabs using SLABCUT keyword, whether the surface slab is directly a free standing slab(i.e.,non-periodic slab with periodicity breaking along the out of plane direction), or it is periodic slab and to break the periodicity we need to create vaccuum along c-axis..

Here is an example of my input geometry:

[...]
SLABCUT
0 0 1
1     7
[...]

Since, the in the output z-axis lattice constant is given as 500Angstom.

PS: If it is periodic slab then can anyone guide me to create vaccuum in the c-axis from the input....

Best wishes,
R.Zosiamliana
PSRC
Pachhunga University College

GiacomoAmbrogio

Hi R.Zosiamliana,

When using SLABCUT from a 3D system, or directly a SLAB input, CRYSTAL treats the resulting system as a lower-dimensional 2D structure. Specifically, the system retains periodicity only along two directions (conventionally in the x-y plane), while periodicity is inherently absent along the orthogonal direction (z).

Just to preserve the same output format as for a 3D calculation, an arbitrary value of 500 Å is printed in the output for the c lattice vector, even if it does not exist for such calculations. We understand this may be confusing and we are considering to remove it in future versions.

To summarise, in CRYSTAL when running a 2D (or 1D, or 0D) calculation, there is no need to repeat the structure along the non-periodic direction and thus there is no need to define a vacuum.

R.Zosiamliana

Thank you Giacomo Ambrogio.
I am greatful to the CRYSTAL code forum
This will help alot.

Best Wishes