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26 lines
1.3 KiB
Plaintext
26 lines
1.3 KiB
Plaintext
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This example shows how to use pw.x to optimize crystal structures at two
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pressures for As. Arsenic is well known to undergo a phase transition from
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A7 structure to imple cubic at about 30 GPa. (See da Silva CR, Wentzcovitch RM,
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COMPUTATIONAL MATERIALS SCIENCE 8 (3): 219-227 JUL 1997).
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1) make a vc-relax calculation with external (target) pressure = 0 kbar, using
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Wentzcovitch dynamics (cell_dynamics = 'damp-w' in CELL namelist),
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(input=As.vcs00.in, output=As.vcs00.out). In this case, the angle between
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cell vectors at the end of the calculation is 58 degrees and the internal
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coordinate is 0.2723, typical of A7 structure.
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2) make a vc-relax calculation with external (target) pressure = 500 kbar, also
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using Wentzcovitch dynamics. (input=As.vcs500.in, output=As.vcs500.out). In
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this case, the angle between cell vectors at the end of the calculation is
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60 degrees and the internal coordinate is 0.25, typical of sc structure.
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Both calculations start from the same initial structure with an angle of
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60 degrees between vectors and internal coordinate 0.290010 .
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PLEASE NOTE: the structure has "ibrav=-0", that is, it is read from cards
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"CELL_PARAMETERS". Only the lattice parametr "A" is used; the other
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cell parameters B, C, COSAB COSAC, COSBC are reported for convenience,
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but thay are neither read nor used
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