@article { ISI:000306111900003,
	title = {Extended coupled cluster for Raman and infrared spectra of small molecules},
	journal = {Chemical Physics},
	volume = {403},
	year = {2012},
	month = {JUL},
	pages = {25-32},
	publisher = {ELSEVIER SCIENCE BV},
	address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS},
	abstract = {<p>In this paper we study the harmonic vibrational frequencies, infrared (IR) intensities, Raman intensities and depolarization ratio using extended coupled cluster method. Raman and IR intensities are mixed derivatives of energy with respect to the electric field and geometric perturbation whereas vibrational frequencies are derivatives of energy with respect to geometry. We use semi-numerical approach to obtain these derivatives. We have studied the effect of electron correlation and basis set for the above properties. We compare our results with non-variational coupled cluster and experimental values, wherever available. We have studied HF, BH, CH+, CO and H2CO molecules in different basis sets. For HF molecule, benchmarking is done with full CI values and basis set convergence is studied for this molecule. Effect of triples is studied for all the molecules. (C) 2012 Elsevier B.V. All rights reserved.</p>},
	keywords = {Extended coupled cluster, IR and Raman spectroscopy, Mixed derivatives},
	issn = {0301-0104},
	doi = {10.1016/j.chemphys.2012.04.017},
	author = {Joshi, Sayali P. and Dutta, Achintya Kumar and Pal, Sourav and Vaval, Nayana}
}
@article { ISI:000319006300007,
	title = {Extended coupled cluster through nth perturbation order for molecular response properties: a comparative study},
	journal = {Chemical Physics},
	volume = {417},
	year = {2013},
	month = {MAY},
	pages = {45-51},
	publisher = {ELSEVIER SCIENCE BV},
	address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS},
	abstract = {<p>In this paper, we have presented and analyzed the extended coupled cluster (ECC) energy functional, truncated up to nth perturbation order in which expansion is limit to operators of the single and double excitations. The expression for the first order energy derivatives based on the above truncation schemes has been derived and numerically analyzed. We have done a comparative study for dipole moment in various perturbative ECC (n) methods (2 \&lt;= n \&lt;= 5) for three systems (HF, H2O and BH) at equilibrium geometry. We have particularly studied two variants of ECC (4) and ECC (5*) method for stretched geometry. We have analyzed the contribution of important terms present in ECC functional based on perturbative argument. We have compared our results with standard coupled cluster (CCSD) as well as cubic truncated ECC and also benchmarked with the full CI results wherever available. (c) 2013 Elsevier B.V. All rights reserved.</p>},
	keywords = {Dipole moment, Energy functional, Extended coupled cluster},
	issn = {0301-0104},
	doi = {10.1016/j.chemphys.2013.03.012},
	author = {Gupta, Jitendra and Manohar, Prashant Uday and Ghosh, Aryya and Vaval, Nayana and Pal, Sourav}
}
