@article {43243,
	title = {Study of cumulant approximations to n-electron valence multireference perturbation theory},
	journal = {Journal of Chemical Physics},
	volume = {130},
	year = {2009},
	month = {MAY},
	pages = {Article Number: 194107},
	abstract = {We investigate the possibility of reducing the complexity of multireference perturbation theory through cumulant based approximations to the high-order density matrices that appear in such theories. Our test cases show that while the cumulant approximated forms are degraded in accuracy relative to the parent theory and exhibit intruder state problems that must be carefully handled, they may provide a route to a simple estimation of dynamic correlation when the parent perturbation theory is infeasible. Nonetheless, further work is clearly needed on better approximations to the denominators in the perturbation theory.},
	doi = {10.1063/1.3132922},
	author = {Zgid, Dominika and Ghosh, Debashree and Neuscamman, Eric and Chan, Garnet Kin-Lic}
}
@article { ISI:000352270700029,
	title = {Singlet-triplet gaps in polyacenes: a delicate balance between dynamic and static correlations investigated by spin-flip methods},
	journal = {Physical Chemistry Chemical Physics},
	volume = {17},
	number = {15},
	year = {2015},
	month = {MAR},
	pages = {9849-9856},
	publisher = {ROYAL SOC CHEMISTRY},
	address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND},
	abstract = {<p>Over the last few years people have been interested in the process of singlet fission, owing to its relevance to solar cell technology. The energetics of singlet fission is intimately related to singlet-triplet (ST) gaps and energies of singlet excited states. However, accurate calculations of ST gaps in polyacenes are complicated due to near degeneracies in the pi orbitals, and therefore, have been quite challenging. The spin-flip equation-of-motion coupled-cluster (SF-EOM-CC) and its perturbative approximation have been shown to correctly treat situations involving electronic degeneracies and near degeneracies. In this work, we use various spin-flip methods to benchmark the ST gaps of small polyacenes and show that the error in the ST gaps with respect to the experiment is small and does not increase appreciably with the system size. The diradical and polyradical character of the polyacene ground states increase with the system size. However, for the small polyacenes the open-shell character of the ground state is still small enough to be treated using single reference methods.</p>},
	issn = {1463-9076},
	doi = {10.1039/c5cp00214a},
	author = {Ibeji, Collins U. and Ghosh, Debashree}
}
@article { ISI:000346235600046,
	title = {Spectroscopic and ab initio investigation of 2,6-difluorophenylacetylene-amine complexes: coexistence of C-H center dot center dot center dot N and lone-pair center dot center dot center dot pi complexes and intermolecular coulombic decay},
	journal = {Physical Chemistry Chemical Physics},
	volume = {17},
	number = {1},
	year = {2015},
	month = {OCT},
	pages = {434-443},
	publisher = {ROYAL SOC CHEMISTRY},
	address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND},
	abstract = {<p>Binary complexes of 2,6-difluorophenylacetylene with methylamine, dimethylamine, trimethylamine and triethylamine were investigated using one colour resonant two photon ionization and infrared-optical double resonance spectroscopic techniques combined with high level ab initio calculations. All four amines form C-Ac-H center dot center dot center dot N hydrogen-bonded complexes. Additionally trimethylamine and triethylamine form complexes characterized by Lp center dot center dot center dot pi interactions, due to the electron deficient nature of the phenyl ring of 2,6-difluorophenylacetylene. The Lp center dot center dot center dot pi interacting structure of the 2,6-difluorophenylacetylenetrimethylamine complex is about 1.5 kJ mol(-1) higher in energy than the C-Ac-H center dot center dot center dot N hydrogen-bonded structure, which is the global minimum. Energy decomposition analysis indicates that the electrostatics and dispersion interactions favour the formation of C-Ac-H center dot center dot center dot N and Lp center dot center dot center dot pi complexes, respectively. Interestingly the C-Ac-H center dot center dot center dot N hydrogen-bonded complex of 2,6-difluorophenylacetylene-triethylamine showed a smaller shift in the acetylenic C-H stretching frequency than the 2,6-difluorophenylacetylene-trimethylamine complex. The observed fragmentation of the binary complexes of 2,6-difluorophenylacetylene with the four amines following resonant two-photon ionization can be explained on the basis of the intermolecular coulombic decay process.</p>},
	issn = {1463-9076},
	doi = {10.1039/c4cp03445g},
	author = {Mondal, Sohidul Islam and Dey, Arghya and Sen, Saumik and Patwari, G. Naresh and Ghosh, Debashree}
}
