$ # Before install, check the spec using specific version of fftw
$ spack spec namd@2.12 ~cuda fftw=3 interface=python ^fftw@3.3.4 +mpi +openmp +pfft_patches ^mpich@3.4.1
Input spec
--------------------------------
namd@2.12~cuda fftw=3 interface=python
    ^fftw@3.3.4+mpi+openmp+pfft_patches

Concretized
--------------------------------
namd@2.12%gcc@11.2.0~cuda cuda_arch=none fftw=3 interface=python arch=linux-sles15-zen3
    ^charmpp@6.7.1%gcc@11.2.0~cuda~omp~papi+production~pthreads+shared+smp~syncft~tcp~tracing backend=netlrts build-target=LIBS patches=92d507d8b72ac01f114f7772510049cc7656f93daeadef46e1f2b00ad8533d2b,e636c3f88a6944c87d910d4c8fdf25146b60f57e09228497a6cc01c7dbae9569 pmi=none arch=linux-sles15-zen3
    ^fftw@3.3.4%gcc@11.2.0+mpi+openmp+pfft_patches patches=4c813199aa39c0d2b23259ee3c3a58c9c96a3c0d09fe3485a33f299b95e0d9e7 precision=double,float arch=linux-sles15-zen3
        ^autoconf@2.69%gcc@11.2.0 arch=linux-sles15-zen3
        ^automake@1.15.1%gcc@11.2.0 arch=linux-sles15-zen3
        ^libtool@2.4.6%gcc@11.2.0 arch=linux-sles15-zen3
        ^mpich@3.4.1%gcc@11.2.0~argobots+fortran+hwloc+hydra+libxml2+pci+romio+slurm~verbs+wrapperrpath device=ch4 netmod=ofi pmi=pmi arch=linux-sles15-zen3
    ^python@3.6.13%gcc@11.2.0+bz2+ctypes+dbm~debug+libxml2+lzma+nis~optimizations+pic+pyexpat+pythoncmd+readline+shared+sqlite3+ssl~tix~tkinter~ucs4+uuid+zlib arch=linux-sles15-zen3
    ^tcl@8.6.11%gcc@11.2.0 arch=linux-sles15-zen3
        ^zlib@1.2.11%gcc@11.2.0+optimize+pic+shared arch=linux-sles15-zen3
$ # the spec looks okay, let's install it
$ sg <projectcode> -c 'spack install namd@2.12 ~cuda fftw=3 interface=python ^fftw@3.3.4 +mpi +openmp +pfft_patches'

Spack would normally download the source code for any packages that it needs to install. The source code for NAMD has a particular restriction that it cannot be downloaded by spack but must be obtained separately:

$ sg <projectcode> -c 'spack install namd@2.12 ~cuda fftw=3 interface=python ^fftw@3.3.4 +mpi +openmp +pfft_patches'
...
==> Installing namd-2.12-tey6bdfijoegx3dkxfc553nckfecmhku
==> No binary for namd-2.12-tey6bdfijoegx3dkxfc553nckfecmhku found: installing from source
...
==> Error: FetchError: Manual download is required for namd. Refer to http://www.ks.uiuc.edu/Research/namd/ for download instructions.

This can be addressed by first manually downloading the source tarball into your current directory where spack will detect it.

If your module is not being listed by the module avail command, it is very possible that Lmod is forcing the use of the cache instead of a real new search of installed modules. Then we recommend to remove the old cached list of modules, forcing Lmod to search again for the currently installed modules including the recently created ones. For that, users should simply delete the existing Lmod cache with the following command:

rm -rf ~/.cache/lmod
rm -rf ~/.lmod.d/.cache