The VTST•Tools has a fortran component which can be linked into the VASP code as well as a collection of scripts.
In VTST v2.04 and later, a modification is required in main.F for the solid-state NEB.
Find and replace:
CALL CHAIN_FORCE(T_INFO%NIONS,DYN%POSION,TOTEN,TIFOR, &
LATT_CUR%A,LATT_CUR%B,IO%IU6)
with
CALL CHAIN_FORCE(T_INFO%NIONS,DYN%POSION,TOTEN,TIFOR, &
TSIF,LATT_CUR%A,LATT_CUR%B,IO%IU6)
For vasp.6.2 and later, also find and replace:
IF (LCHAIN) CALL chain_init( T_INFO, IO)
with
CALL chain_init( T_INFO, IO)
For vasp.6.2.1 you will need vtstcode 4.1 (revision 182). A version of the vtstcode that will work with vasp.6.1.x - vasp.6.2.0 has been saved in the vtstcode6.1 directory.
The vtstcode6.3 directory contains a machine learning optimizer (IOPT=8) that has been recently added. Follow the instruction according to the version that is used.
The code for the NEB, dimer, Lanczos, and dynamical matrix methods, as well as the steepest descent, force-based conjugate gradient, quick-min, lbfgs, bfgs, and fire optimizers are contained in a single package which interfaces to VASP through the chain.F file.
To install, download the files in vtsttools/vtstcode, choose a version, and copy the files in the directory into your vasp source directory. The file chain.F is replaced, so back up the old version. There are other files in the package: neb.F, dynmat.F, dimer.F, lanczos.F, sd.F, cg.F, qm.F, lbfgs.F, bfgs.F, fire.F, and opt.F in vtstcode5/ and vtstcode6.1/ directories. The vtstcode6.3/ directory contains another file called ml_pyamff.F and directory named pyamff_fortran/, which interface to a machine learning package PyAMFF.
To build the code, the VASP .objects and makefile need to be changed. Find the variable SOURCE in the .objects file (a hidden file in src/), which defines which objects will be built, and add the following objects before chain.o:
vtstcode5 and vtstcode6.1
bfgs.o dynmat.o instanton.o lbfgs.o sd.o cg.o dimer.o bbm.o \
fire.o lanczos.o neb.o qm.o opt.o
vtstcode6.3
bfgs.o dynmat.o instanton.o lbfgs.o sd.o cg.o dimer.o bbm.o \
fire.o lanczos.o neb.o qm.o \
pyamff_fortran/*.o ml_pyamff.o \
opt.o
The objects dynmat.o, neb.o, dimer.o, lanczos.o, and instanton.o must be in the SOURCE list before chain.o appears. The optimizer objects, sd.o, cg.o, qm.o, lbfgs.o, bfgs.o, fire.o (vtstcode 5 and vtstcode 6.1), ml_pyamff.o and all the objects in the pyamff_fortran/ directory (vtstcode 6.3) must appear before the optimizer driver opt.o.
If you use vtstcode6.3, you need one more modification. Find the variable LIB in makefile that is inside src/, and add the following directory after the last element of the list of library:
vtstcode6.3
LIB= lib parser pyamff_fortran
If you compile in parallel, you need to add libs to your dependencies in makefile:
dependencies: sources libs
Nothing else needs to be done. This code will not change the working of any other part of vasp. This code will only be run if IMAGES is set in the INCAR file, or if ICHAIN is set, to specify which method should be run.
ICHAIN=0: Nudged elastic band (default)
ICHAIN=1: Dynamical matrix
ICHAIN=2: Dimer
ICHAIN=3: Lanczos