You can find instructions to build Vasp with support for DFT-D4 in the main repository at dftd4/dftd4. Follow the instructions in the README to build dftd4 and make it available in Vasp.

Get your copy of the dftd4 code and install the code to obtain a shared library. Tested using ifort (18.0.2).

FC=ifort CC=icc CXX=icpc meson setup build && ninja -C build
mkdir install
DESTDIR=/path/to/staging/area/install ninja -C build install

Extend your PATH by the build directory and be sure the shared library is available for linking purposes.

Modify your makefile.include

# Precompiler options
CPP_OPTIONS= -DHOST=\"LinuxIFC\"\
             -DMPI -DMPI_BLOCK=8000 \
             -Duse_collective \
             -DscaLAPACK \
             -DCACHE_SIZE=4000 \
             -Davoidalloc \
             -Duse_bse_te \
             -Dvasp6 \
             -Dtbdyn \
             -DWITH_DFTD4
# dftd4 path
DFTD4_PATH =/path/to/staging/area/install/usr/local
DFTD4      =-ldftd4 -L${DFTD4_PATH}/lib64/

LLIBS      = ...all libs...  $(DFTD4)
INCS       = ...all modules... -I${DFTD4_PATH}/include

Within src/.objects add "subdftd4.o" below "subdftd3.o".

Add the dftd4 module within src/vdwforcefield.F by incorporating it with "USE vdwD4".

Within the "vdw_forces_main" subroutine, add a new IVDW case for dftd4 just below the one of dftd3, which has "CASE(12)".

! D4-ATM(EEQ) implemented by Eike Caldeweyher
CASE(13)
  CALL vdw_forces_D4(IO,LATT_CUR,DYN,T_INFO,TSIF,TIFOR,TOTEN,ELEM,IVDW)

Within the "vdw_read" subroutine, add the dftd4 case (IVDW=13). After processing the INCAR file this can easily be added:

IF (IVDW==1 .OR. IVDW==2 .OR. IVDW==3 .OR. IVDW==4 .OR. (IVDW>=10 .AND. IVDW<=13) .OR.  &
&   IVDW==101 .OR. (IVDW>=20 .AND. IVDW<=22) .OR. IVDW==26 .OR.  IVDW==202 &
&   .OR. IVDW==212 .OR. IVDW==263 .OR. IVDW==612  ) THEN
  LVDW=.TRUE.
ELSE
  LVDW=.FALSE.
  CALL PROCESS_INCAR(LOPEN, IO%IU0, IO%IU5, 'LVDW', LVDW, IERR, WRITEXMLINCAR)
  IF (LVDW) IVDW=1
ENDIF

This implementation is tested for VASP 6.0.X versions. For earlier VASP versions take care of the vtutor module, which is used within the subdftd4.F file. vtutor is not available in those versions (comment out those parts).

Always cite:

Eike Caldeweyher, Christoph Bannwarth and Stefan Grimme, J. Chem. Phys., 2017, 147, 034112. DOI: 10.1063/1.4993215

Eike Caldeweyher, Sebastian Ehlert, Andreas Hansen, Hagen Neugebauer, Sebastian Spicher, Christoph Bannwarth and Stefan Grimme, J. Chem Phys, 2019, 150, 154122. DOI: 10.1063/1.5090222 chemrxiv: 10.26434/chemrxiv.7430216

Eike Caldeweyher, Jan-Michael Mewes, Sebastian Ehlert and Stefan Grimme, Phys. Chem. Chem. Phys., 2020, 22, 8499-8512. DOI: 10.1039/D0CP00502A chemrxiv: 10.26434/chemrxiv.10299428

please report all bugs with an example input and the used geometry to me or open an issue.