State‐specific multireference perturbation theory: development and present status

• DOI: 10.1002/wcms.1248
• Publication Date: 2016-02-05T08:09:07Z
• Authors: Sudip Chattopadhyay; Rajat K Chaudhuri; Uttam Sinha Mahap...; Anirban Ghosh; Suvonil Sinha Ray
• Keywords: 02 engineering and technology; 0210 nano-technology

The state‐specific multireference perturbation theory ( SSMRPT ), which provides one state at a time may now gradually become new useful ab initio tool for studying electronic states with strong configurational quasidegeneracy owing primarily to its suitability toward numerical implementation in the presence of intruders and also great extent firm theoretical construct scope systematic hierarchical improvement. method works complete active space, treats each model space functions on same footing by exploiting Jeziorski–Monkhorst parametrization wavefunction. is size‐extensive size‐consistent (with orbitals localized). real challenge remains developing MRPT methods capable maintaining explicit size‐extensivity avoiding over vast range molecular geometries. Recently developed relativistic four‐component spinors very promising describe near‐degenerate molecules containing heavy atoms. analysis formal aspects practical utility vis‐à‐vis other formalisms that bear kinship formulation presented. Illustrative results show high accuracy describing quasidegenerate situations such as those appearing when or more covalent bonds molecule stretched broken. While actively pursuing method, it became apparent us this encounters two major limitations: (1) scaling computational cost respect number (2) lack invariance energy unitary transformation orbitals. future will tell whether be able acquire faith widely used single‐root methods. WIREs Comput Mol Sci 2016, 6:266–291. doi: 10.1002/wcms.1248 This article categorized under: Electronic Structure Theory > Ab Initio Methods