PNNL-13501 - Pacific Northwest National Laboratory

Water
Figure 1. Schematic representation of the partition of a
mineral/water/pollutant interface region
Massively Parallel Projector-Augmented-Wave Program
Over the past year, with the help of M. Valiev at the
University of California, San Diego, we developed and
coded a parallel projecter-augmented-wave method. This
code was based on a serial FORTRAN 90 code written by
M. Valiev. The code was parallelized using the Message
Passing Interface standard library and uses a slabdecomposed
Fast-Fourier Transform module written by E.
J. Bylaska. The code gives good parallel performance,
and compares well to other plane-wave methods.
We performed simulations on a variety of molecular
systems using the parallel projector-augmented-wave
code. Our results showed that
• The accuracy of the code is similar to the density
functional calculations based on local basis sets.
• The convergence with respect to the plane-wave basis
set leads to practical calculations, even for very
difficult systems (F, O, Fe, Cr).
• The method is robust with respect to the choice of the
local basis set.
• For a given plane-wave basis set size, the execution
times of projector-augmented-wave calculations are
similar to those of pseudopotential plane-wave
methods.
• The size of the plane-wave basis is smaller compared
to the norm-conserving pseudopotential plane-wave
method.
QM
Mineral
Free-Space Boundary Conditions
Our proposed quantum mechanics/molecular mechanics
development requires that the quantum mechanics system
is solved using free-space boundary conditions. During
the last year, we developed a technique to implement freespace
boundary conditions into plane-wave methods.
Equations providing a highly accurate implementation
were developed (see Figure 2). We showed that the
energies calculated using a modified free-space planewave
code could be directly compared to a conventional
periodic plane-wave code for problems in which the
choice of boundary conditions was not important.
Furthermore, implementing free-space boundary
conditions into an existing parallel periodic plane-wave
code would not significantly degrade its parallel
efficiency.
Figure 2. Error in calculating the electron-electron Coulomb
energy for a test density composed of three normalized
Gaussian functions located at (8.0,8.0,10.0), (12.0,12.0,12.0),
and (8.0,13.0,10.0) on the W=[0.0,20.0) 3 domain. The
normalized Gaussians have decay rates of 0.4, 0.4, and 0.5
respectively. A dramatic increase in accuracy is seen with
our developed formula (legend: Eq. 15 and 17) compared
with other published formula (legend: Eq. 12 and 16).
Studies of Iron-Oxides
Studies of iron-oxides were performed using traditional
pseudopotential plane-wave methods. Pseudopotential
plane-wave methods were used to investigate the
structures and total energies of AlOOH and FeOOH in the
five canonical oxyhydroxide structures: diaspore
(goethite), boehmite (lepidocrocite), akaganeite,
Computational Science and Engineering 139