## Superposition of Fragment Excitations for Excited States of Large Clusters with Application to Helium Clusters

journal contribution

posted on 08.12.2015 by Kristina
D. Closser, Qinghui Ge, Yuezhi Mao, Yihan Shao, Martin Head-Gordon#### journal contribution

Any type of content formally published in an academic journal, usually following a peer-review process.

We develop a local excited-state
method, based on the configuration
interaction singles (CIS) wave function, for large atomic and molecular
clusters. This method exploits the properties of absolutely localized
molecular orbitals (ALMOs), which strictly limits the total number
of excitations, and results in formal scaling with the third power
of the system size for computing the full spectrum of ALMO–CIS
excited states. The derivation of the equations and design of the
algorithm are discussed in detail, with particular emphasis on the
computational scaling. Clusters containing ∼500 atoms were
used in evaluating the scaling, which agrees with the theoretical
predictions, and the accuracy of the method is evaluated with respect
to standard CIS. A pioneering application to the size dependence of
the helium cluster spectrum is also presented for clusters of 25–231
atoms, the largest of which results in the computation of 2310 excited
states per sampled cluster geometry.