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- Lindh, Roland, 1958-, et al.
(författare)
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The energy separation between the classical and nonclassical isomers of protonated acetylene : An extensive study in one‐ and n‐particle space
- 1991
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 94:12, s. 8008-8014
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Tidskriftsartikel (refereegranskat)abstract
- The energy separation between the classical and nonclassical forms of protonated acetylene has been reinvestigated in light of the recent experimentally deduced lower bound to this value of 6.0 kcal/mol. The objective of the present study is to use state-of-the-art ab initio quantum mechanical methods to establish this energy difference to within chemical accuracy (i.e., about 1 kcal/mol). The one-particle basis sets include up to g-type functions and the electron correlation methods include single and double excitation coupled-cluster (CCSD), the CCSD(T) extension, multireference configuration interaction, and the averaged coupled-pair functional methods. A correction for zero-point vibrational energies has also been included, yielding a best estimate for the energy difference between the classical and nonclassical forms of 3.7 +/- 1.3 kcal/mol.
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| 2. |
- Rendell, Alistair P, et al.
(författare)
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Quantum chemistry on parallel computer architectures : oupled-cluster theory applied to the bending potential of fulminic acid
- 1992
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 194:1-2, s. 84-94
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Tidskriftsartikel (refereegranskat)abstract
- We present a formulation of the singles and doubles coupled-cluster (CCSD) method suitable for distributed memory parallel computer architectures. Results from test calculations using up to 128 nodes of the Intel i860 hypercube are presented. Although the new algorithm is highly parallel, the asymptotic speed is quickly reached due to the input/output (IO) demands on the concurrent file system. To alleviate these IO problems, as well as disk storage requirements, we propose a “semi-direct” CCSD method whereby the atomic orbital integrals are evaluated in each iteration of the procedure in order to determine the contribution from certain terms. Using CCSD(T)/TZ2P optimized geometries, the calculations show that the Born-Oppenheimer ground-state potential energy surface yields a linear structure for fulminic acid. HCNO, in agreement with the semirigid bender analysis by Bunker, Landsberg and Winnewisser.
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