UT theoretical chemistry code forum

Dear guys,

In the webpage: viewtopic.php?f=2&t=329, Prof. Graeme mentions that after finding the initial state and transition state, I should perform two seperate dynamical matrix calculations, one for initial state and another for transition state. Both dynamical matrix calculations need a DISPLACECAR file as a input file besides regular VASP input files - INCAR, KPOINTS, POSCAR and POTCAR.

If I choose to use the dymseldsp.pl script to generate the DISPLACECAR file, I issue the command:
dymseldsp.pl (POSCAR 1) (POSCAR 2) (atoms to include) (displacement)
where POSCAR 1 is the configuration of initial state and POSCAR 2 is that of transition state.

My questions are as follows:
1. Does that mean that both dynamical matrix calculations will use the same DISPLACECAR file?

2. Are the "atoms to include" the atoms that will displace a lot between initial state and transition state? Do I have to specify this parameter? what will happen if I don't?

3. What is the unit of (displacement)? Angstrom? Does it have a default value? what will happen if I don't specify a value?

Thanks.

1. Yes, both transition state and initial state can use the same DISPLACECAR.

2. In the dymseldsp.pl, the number of atoms is required; it will select that number of atoms that are displaced the most between the initial state and saddle point. An even simpler way of running is to select all of the non-frozen atoms, although this can be more expensive for large systems.

3. Angstroms. You should choose a value between 0.05 and 0.001 and make sure that the modes you calculate are insensitive to making the displacement smaller.

Hi Prof. Graeme, I appreciate you replies which help me so much.