PNNL-13501 - Pacific Northwest National Laboratory

guyanaite, and grimaldiite (see Figure 3). The local
density approximation was used in conjunction with ultrasoft
pseudopotentials in full optimizations of both AlOOH
and FeOOH in each of these structures. Structures are in
reasonably good agreement with experiment, with lattice
parameters and bond lengths within 3% of the
experimental ones. However, the relative energetics
between the isomorphic structures only converged for the
AlOOH structures and not the FeOOH structures,
regardless of the type of pseudopotential or exchangecorrelation
functional used. This indicates the need for
highly accurate methods like projector-augmented-wave,
to assess relative energetics between FeOOH isomorphic
structures.
Figure 3. Iron-oxide and aluminum-oxide polymorphs
studies using pseudopotential plane-wave methods
Water Pseudopotentials
With the completion of our parallel projector-augmentedwave
code, we recently began to incorporate a water
pseudpotential. Our current results suggest that our water
pseudopotential is numerically stable and induces the
correct polarization (see Figure 4). We have already
incorporated most of the quantum mechanics/molecular
mechanics interactions needed to describe a quantum
mechanics water and molecular mechanics water. We are
currently parameterizing the van der Waal’s interaction
between the quantum mechanics and molecular
mechanics part using the water dimer.
Summary and Conclusions
A massively parallel projector-augmented-wave program
was developed and tested. It has proven effective for
systems containing first-row transition-metals, which are
difficult to treat with traditional plane-wave methods. In
addition, important new capabilities were added to the
program. Our program can handle free-space boundary
140 FY 2000 Laboratory Directed Research and Development Annual Report
conditions and periodic boundary conditions on equal
footing. Finally, the addition of water pseudopotentials to
the projector-augmented-wave program will allow ab
initio solvation studies to be performed at a lower cost.
Figure 4. Comparison of the density polarization from a
water molecule described by quantum mechanics (top
figure) and by a pseudopotential (bottom figure). Each
contour plot shows the electron density of a water molecule
polarized by another water molecule (quantum mechanics
and pseudopotential, R OO=2.7Å.).
In FY 2001, this project will develop an embedding
procedure to incorporate a classical treatment of longrange
solid-state effects; for example, the surrounding
lattice framework can then be excluded from the planewave
treatment for additonal computational benefit.
References
Blöchl PE. 1994. “Projector augmented-wave method.”
Phys. Rev. B 50:17953-17979.
Gao J and TR Furlani. 1995. “Simulating solvent effects
in organic chemistry: Combining quantum and molecular
mechanics.” In IEEE Comp. Sci. Technol., 24-33.
Presentation
Rustad JR and KM Rosso. April 2000. “Total energy
calculations of iron and aluminum oxyhydroxide bulk
phases and surfaces.” MRS 2000 Spring Meeting, San
Francisco, California.