Hello,

I’m performing a 2D slab calculation using CRYSTAL17 for a hexagonal monolayer system (a = b = 6.81998 Å, γ = 120°, c = 500 Å to simulate vacuum). Geometry is read from an external file. I enabled piezoelectric property calculation.

CRYSTAL printed the piezoelectric tensor (in |e|·bohr units) as:

| 0.000 0.000 -3.931 |
| -3.931 3.931 0.000 |
| 0.083 0.083 0.000 |

My questions:

1) For slab models, should the full 3D volume be used in the unit conversion to C/m2, or just the in-plane area?

2) Are these piezoelectric constants physically meaningful for 2D systems, or is there a standard post-processing correction needed?

Thank you in advance for your help.

Best regards,
R.Zosiamliana
PSRC
3yrs+, CRYSTAL17 user.

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

Best Wishes

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

Thank you Jacques for your kind help.
This will solve multiple problems of my current work

Regards
R.Zosiamliana

Dear Jacques thank you for your help. However, when i come across Chapter10, i could not find convincing input for the above mentioned properties.

I have uploaded the kind of output i required.

I kindly request for your help!!

Best regards,
R.Zosiamliana

Thank you sir for your kind reply...

Dear code developers',

I am currently working on optical materials for optoelectronic device applications using CRYSTAL code. However, I have been unable to find any input files or methods for calculating photon energy (or frequency) versus optical parameters, such as the real and imaginary parts of the dielectric constant, refractive index, extinction coefficient, or optical absorption coefficient.

While reviewing several research articles, I did not come across any studies where optical properties were calculated using the CRYSTAL code.

Therefore, I would like to ask: Is it possible to calculate photon energy vs. optical parameters using the CRYSTAL code? If so, I would greatly appreciate any guidance on how to set up the input file for such calculations.

Thank you in advance for your help!

Best regards,
R. Zosiamliana
Physical Sciences Research Center (PSRC)
Pachhunga University College
Mizoram, India

When calculating the elastic constants (Cij​) for bulk materials, the output values are provided in units of GPa. However, when generating a [0 0 1] surface slab (2D) from the corresponding bulk material using the SLABCUT keyword, the output elastic constant (Cij​) values are given in Hartree (Ha).

Could anyone please clarify whether these values are expressed in Ha/Bohr² or Ha/Ų, considering that the conventional SI unit for surface (Cij) in 2D materials is N/m?

here is my output comparison between bulk and 2D surface

For Bulk
SYMMETRIZED ELASTIC CONSTANTS FOR CUBIC CASE, IN GPa

| 121.241 47.439 47.439 0.000 0.000 0.000 |
| 121.241 47.439 0.000 0.000 0.000 |
| 121.241 0.000 0.000 0.000 |
| 71.165 0.000 0.000 |
| 71.165 0.000 |
| 71.165 |
For 2D-surface
SYMMETRIZED ELASTIC CONSTANTS FOR TRICLINIC CASE, IN HARTREE

| 2.059 0.349 0.000 |
| 2.059 0.000 |
| 1.099 |