In fact，by doing my experiment ，I found that there are two types of crystals in one system。And a series of phenomena was found that interested myself，so I want to calculate the defect formation energies by using VASP。As far as I know，the vasp can handle calculations relating to heterojunctions ，but the models used in heterojunctions calculations are 2D structures。I don't know whether such models can be able to handle defect formation energies calculation of two crystals，or is there any other way to simulate the condition ？
The crystal systems of them are orthorhombic and trigonal。
Thanks for your help。
VASP calculations rely on periodic boundary conditions and, as such, can allow only one set of lattice parameters in one calculation. The only way to calculate the electronic structure of a heterostructure is to construct a slab, but that requires breaking translational symmetry along one direction and adding a vacuum barrier to avoid periodic interactions between two domains.
Yes, if there are two domains with different crystal structures in a sample, the interactions between them happen through their interface. This can be modelled by appropriately stacking the two materials in a double slab. Importantly, the slab must contain sufficient number of layers from each material to account for their individual bulk properties and a large enough vacuum barrier to avoid interaction between them from anywhere else other than the interface.
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