Dear friends,
When I query the stable elements by API by the below code:
from mp_api.client import MPRester
with MPRester(“API_Key”) as mpr:
docs = mpr.summary.search(num_elements=(1,1),chemsys=“Si”,
energy_above_hull=(0,0),
fields=[“material_id”])
mpid_formula_dict = {doc.material_id for doc in docs}
for item in mpid_formula_dict:
structure = mpr.get_structure_by_material_id(item)
structure.to( filename=‘POSCAR’)
I get the below poscar file:
Si2
1.0
3.3335729999999999 0.0000000000000000 1.9246390000000000
1.1111910000000000 3.1429239999999998 1.9246390000000000
0.0000000000000000 0.0000000000000000 3.8492780000000000
Si
2
direct
0.8750000000000000 0.8750000000000000 0.8750000000000000 Si
0.1250000000000000 0.1250000000000000 0.1250000000000000 Si
But when using the MP website for stable Si structure that it’s Ehull equal to zero but the stable one is the below structure:
Si8
1.0
5.4437023729394527 0.0000000000000000 0.0000000000000003
0.0000000000000009 5.4437023729394527 0.0000000000000003
0.0000000000000000 0.0000000000000000 5.4437023729394527
Si
8
direct
0.7500000000000000 0.7500000000000000 0.2500000000000000 Si
0.0000000000000000 0.5000000000000000 0.5000000000000000 Si
0.7500000000000000 0.2500000000000000 0.7500000000000000 Si
0.0000000000000000 0.0000000000000000 0.0000000000000000 Si
0.2500000000000000 0.7500000000000000 0.7500000000000000 Si
0.5000000000000000 0.5000000000000000 0.0000000000000000 Si
0.2500000000000000 0.2500000000000000 0.2500000000000000 Si
0.5000000000000000 0.0000000000000000 0.5000000000000000 Si
As you saw the only stable (Ehull=0) is above the structure of Si. I do not know how this difference takes place and which one is the main structure that you use as the base structure for the calculation of total energy for formation energy.
Of course, a similar question asks “Structure from API and that from Website differ” but I can not sure about the correct structure and I need to know which one is the best one for calculating the formation energy of materials with Si components.
Thank you in advance for your guidance.