ELEMENT_MIX

ELEMENT_MIX defines whether sites defined as one element in the POSCAR file are occupied by multiple chemical elements. See also this page for instructions on how to vary the occupation of a site during structure optimization.

Default: None of the elements given in the POSCAR file are occupied by multiple elements.

Syntax:

ELEMENT_MIX A = La Sr

In the example, the element A should be an element defined in the POSCAR file as the element for a list of sites, while La and Sr are the elements that actually occupying these sites. In the POSCAR file, an atom in a given site can only belong to one element. ELEMENT_MIX allows assigning a site to multiple elements, which can have different properties (e.g., vibrational amplitudes), and read different phase-shift files during the LEED calculation. The elements on the right-hand side should be actual chemical elements, with the two-letter abbreviation as it is found in the periodic table. ELEMENT_MIX is complementary to ELEMENT_RENAME, so no POSCAR element for which ELEMENT_MIX is defined should appear as an ELEMENT_RENAME parameter, and vice versa.

Acceptable values: Due to current limits in the code, a maximum of five different species can occupy one site. If the occupations of the elements defined in the in the VIBROCC file sum to less than one, one of the five species will be a vacancy, so only four different elements can occupy one site if their occupations do not sum to one.

If element splits for multiple elements of the POSCAR file are being defined, have multiple lines starting with ELEMENT_MIX and the respective POSCAR elements left of the ‘=’ sign.

It is recommended to avoid overlap in the element names, e.g., ELEMENT_MIX La = La Sr. For more on this, see the page on element name collision.

The actual occupations of the split sites are defined in the VIBROCC file, and can be fitting parameters.