first open terminal in ubuntu and paste the following commands and run it:
sudo apt-get install build-essential mpich-bin libmpich1.0-dev mpi-doc fftw2 fftw-dev libxaw7-dev
then setup lammps
for more information use this link:
http://ubuntuforums.org/showthread.php?t=1038282&highlight=install+MPICH+FFTW2+lammps
regards