A module for pw to do transformations between real and reciprocal spaces.

[Qianruipku]

Background

FFT is one of the most popular functions in calculations of the electronic structure. Different from simple fft, we only consider the reciprocal grids in a ball with the radius of GCUT. In other words, the values of reciprocal grids out of the GCUT ball (|G+K|>GCUT) are zeros. A module to treat this special FFT is needed.

Describe the solution you'd like

A new class which can do transformations btween the reciprocal and real space.
Parallel program is required.

[Qianruipku]

#418 add pw_basis_k class
#420, #430, #432, #435 add fft in pw module
#448 can first be compiled
#463, #476,#480, #483, #485 add mpi and tests, tests are passed.
#490, #494, #500, #505, #507 change some places to reach higher efficiency
#509 use valgrind to test the memory, the test is passed.
#535, #540, #542, #544, #548, #549 further profiling
#554 add single precision calculation for pw module
#558 add the version compiled without mpi
#593 change fft in x-direction
#598 pw module can execute fft of different k points
#602 merge into develop branch
#618, #620, #623, #629 Rewrite tests in framwork of Gtest

[mohanchen]

@Qianruipku. In your description, I don't know the name of the 'new class', who will provide the solution? you? or, are you asking for help?