IRCCAR

The IRCCAR file defines a discretized transformation path. Usually this is taken from an intrinsic reaction coordinate (IRC - using IBRION=40), projected onto a small set of internal coordinates. It is required to define the path-based coordinates IS and IZ in ICONST.

However, this IRC is followed during a biased molecular dynamics (MD) simulation, similar to the Blue moon ensemble method. The structure of the file is:

M
chi_1(1) chi_2(1) ... chi(r)(1)
chi_1(2) chi_2(2) ... chi(r)(2)
...
chi_1(M) chi_2(M) ... chi(r)(M)

where M is the number of points in the file and chi_j(i) is [math]\displaystyle{ \tilde{\chi}_k(i) }[/math], the discretized transformation path in terms of internal coordinates.

[math]\displaystyle{ \tilde{\chi}_k(i) }[/math] can take values between 0 and 1.

For further information, see pages 50-51 of "Investigating chemical reactions with VASP" .