This data block contains the ionic positions in fractional coordinates.
The POSITIONS_FRAC or POSITIONS_ABS data block is interpreted as the reactant coordinate data for a transition state search.
The data block has the following format:
%BLOCK POSITIONS_FRAC CCC1/I1 R1i R1j R1k CCC2/I2 R2i R2j R2k . . . %ENDBLOCK POSITIONS_FRAC
The first entry on a line is the symbol or atomic number of the ionic species. The correct symbol will be added automatically for atomic species if the atomic number is specified. A symbol can have a maximum of three characters.
The next three entries are real numbers representing the position of the ion in fractions of the unit cell lattice vectors.
Only one of POSITIONS_FRAC and POSITIONS_ABS may be present in a single cell file.
%BLOCK POSITIONS_FRAC . . O 0.7500000000 -0.2500000000 0.2500000000 Al 0.6955000000 0.2500000000 0.9186000000 . . %ENDBLOCK POSITIONS_FRAC
CASTEP keyword glossary
CASTEP cell keywords and data blocks