PMID- 19317531
OWN - NLM
STAT- PubMed-not-MEDLINE
DCOM- 20090507
LR  - 20090325
IS  - 1089-7690 (Electronic)
IS  - 0021-9606 (Linking)
VI  - 130
IP  - 11
DP  - 2009 Mar 21
TI  - A study of the fixed-node error in quantum Monte Carlo calculations of electronic 
      transitions: the case of the singlet n-->pi* (CO) transition of the acrolein.
PG  - 114107
LID - 10.1063/1.3086023 [doi]
AB  - We report fixed-node diffusion Monte Carlo (FN-DMC) calculations of the singlet 
      n-->pi( *) (CO) vertical transition of acrolein. The impact of the fixed-node 
      approximation on the excitation energy is investigated. To do that, trial wave 
      functions corresponding to various nodal patterns are used. They are constructed 
      by using either a minimal complete-active-space self-consistent field (CASSCF) 
      calculation involving an oxygen lone pair n and the pi( *) (CO) molecular 
      orbitals or a more complete set involving all the molecular orbitals expected to 
      play a significant role in the excitation process. Calculations of both states 
      have been performed with molecular orbitals optimized separately for each state 
      via standard "state specific" CASSCF calculations or by using a common set of 
      optimized orbitals ["state averaged" CASSCF calculations] whose effect is to 
      introduce some important correlation between the nodal patterns of the two 
      electronic states. To investigate the role of the basis set three different basis 
      of increasing size have been employed. The comparative study based on the use of 
      all possible combinations of basis sets, active spaces, and type of optimized 
      molecular orbitals shows that the nodal error on the difference of energies is 
      small when chemically relevant active space and state-averaged-type CASSCF wave 
      functions are used, although the fixed-node error on the individual total 
      energies involved can vary substantially. This remarkable result obtained for the 
      acrolein suggests that FN-DMC calculations based on a simple strategy (use of 
      standard ab initio wave functions and no Monte Carlo optimization of molecular 
      orbital parameters) could be a working computational tool for computing 
      electronic transition energies for more general systems.
FAU - Bouabca, Thomas
AU  - Bouabca T
AD  - Laboratoire de Chimie et Physique Quantiques, CNRS-IRSAMC, Universite de Toulouse 
      F-31062, France.
FAU - Ben Amor, Nadia
AU  - Ben Amor N
FAU - Maynau, Daniel
AU  - Maynau D
FAU - Caffarel, Michel
AU  - Caffarel M
LA  - eng
PT  - Journal Article
PL  - United States
TA  - J Chem Phys
JT  - The Journal of chemical physics
JID - 0375360
EDAT- 2009/03/26 09:00
MHDA- 2009/03/26 09:01
CRDT- 2009/03/26 09:00
PHST- 2009/03/26 09:00 [entrez]
PHST- 2009/03/26 09:00 [pubmed]
PHST- 2009/03/26 09:01 [medline]
AID - 10.1063/1.3086023 [doi]
PST - ppublish
SO  - J Chem Phys. 2009 Mar 21;130(11):114107. doi: 10.1063/1.3086023.