Bug #574

Updated by Rossen Apostolov over 8 years ago

Gromacs version 4.5.1 produces zero forces when using Altivec support. From md.log:

Configuring nonbonded kernels...

Configuring standard C nonbonded kernels...

Testing Altivec/VMX support... present.

Configuring PPC/Altivec nonbonded kernels...

The result is that energy minimization fails after a single step:

Steepest Descents converged to Fmax < 1000 in 1 steps

Potential Energy = -2.4873273e+04

Maximum force = 0.0000000e+00 on atom 0

Norm of force = nan

Any resulting simulation crashes immediately, indicating that the structure is insufficiently minimized.

Previous versions of Gromacs worked fine using Altivec support. The mdrun_mpi executable was installed using the following:

./configure --prefix=/home/rdiv1001/gromacs-4.5.1 CPPFLAGS="-I/home/rdiv1001/fftw-3.0.1-osx/include" LDFLAGS="-L/home/rdiv1001/fftw-3.0.1-osx/lib" --disable-threads --without-x --program-suffix=_4.5.1_mpi --enable-mpi CXXCPP="/nfs/compilers/mpich-1.2.5/bin/mpicxx -E"

make mdrun

make install-mdrun

In previous versions of Gromacs, I did not have to specify the CXXCPP environment variable; I don't know if this is related or not.