Basic Research Needs for Solar Energy Utilization - Office of ...

midnight
Sunlight
noon midmidnightnight
165
Sunlight
noon midnight
Energy in Storage
Energy Output
demand Power
Figure 57 Example of the periodic variation of incident sunlight and thermal energy in
the storage, relative to energy demand
SCIENTIFIC CHALLENGE
Theoretical Methods to Identify Photovoltaic Materials with Targeted Properties
Currently, theoretical tools exist that enable first-principles calculation of total-energy and
ground state electronic structure (e.g., density functional theory), but such methods are
computationally very expensive. Even more expensive is accurate calculation of electronic
excited states using, for example,
quantum Monte Carlo methods. Thus,
first-principles theoretical treatment of
systems with many more than 1,000
atoms is currently beyond practicality for
most systems. Thus it is not practical to
use first-principles methods to
exhaustively calculate the atomic and
electronic structure of all possible
photovoltaic materials. Methods that
could circumvent this limit would be
those that enable property-based
identification of promising candidate
materials and then subsequently calculate
electronic structure of a restricted set of
chosen materials (see Figure 58).
Methods to select candidates might
include cluster variation-based methods
and simulated annealing, genetic
algorithms, among others (Franceschetti
and Zunger 1999).
Figure 58 Inverse electronic structure calculations. In
the direct approach, the modeler starts with a given
atomic configuration and calculates the electronic
structure. In the inverse approach, the modeler is told
the electronic structure and must search to find an
atomic configuration that will produce an electronic
structure close to the one required. The inverse
approach is a more difficult challenge.