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71.
72.
Daniel M. Chipman 《Theoretical chemistry accounts》1989,76(2):73-84
Summary The suitability of Gaussian basis sets for ab initio calculation of Fermi contact spin densities is established by application to the prototype first-row atoms B-F having open shell p electrons. Small multiconfiguration self-consistent-field wave functions are used to describe relevant spin and orbital polarization effects. Basis sets are evaluated by comparing the results to highly precise numerical grid calculations previously carried out with the same wave function models. It is found that modest contracted Gaussian basis sets developed primarily for Hartree-Fock calculations can give semiquantitative results if augmented by diffuse functions and if further uncontracted in the outer core-inner valence region. 相似文献
73.
74.
Su-Hong Ge Xin-Lu Cheng Xin-Xing Wang Guang-xing Dong Gui-hua Sun 《Structural chemistry》2007,18(6):985-991
Some explosives are stable molecules with large energy barriers to chemical reaction, and in shock or impact initiation, a
sizable amount of phonon energy must be converted to the molecular internal higher vibrations by multiphonon up pumping. To
investigate the relationship between impact sensitivities and energy transfer rates, the number of doorway modes of explosive
molecules is estimated by a simple theory in which the rate is proportional to the number of normal mode vibrations. We evaluated
frequencies of normal mode vibrations of 13 explosive molecules which are CHNO nitramine-contained and have not been analyzed
previously. The number of doorway modes in the regions of 200–700 cm−1 was evaluated by the direct counting method. For more clear investigation of the relationship we have classified these 13
nitramine explosive molecules, by the number of nitramine group they contained, into two groups. There are eight molecules
that contained one nitramine group and five molecules that contained poly-nitramine groups. It is found that the number of
doorway modes shows a linearly correlation to the impact sensitivities derived from drop hammer tests. This result is in agreement
with that of several previous works. Besides, it is also noted in our study that in those nitramine explosives molecules with
similar molecular structure (similar number nitramine group they contained) and similar molecular weight, the correlation
between the sensitivity and the number of doorway modes is higher. We found that the vibrational frequency of ω corresponds
to nitro group motions of every molecule is contributed to the number of doorway modes in the regions of 200–700 cm−1. 相似文献
75.
De Jong GT Geerke DP Diefenbach A Solà M Bickelhaupt FM 《Journal of computational chemistry》2005,26(10):1006-1020
We have computed a state-of-the-art benchmark potential energy surface (PES) for the archetypal oxidative addition of the ethane C-C bond to the palladium atom and have used this to evaluate the performance of 24 popular density functionals, covering LDA, GGA, meta-GGA, and hybrid density functionals, for describing this reaction. The ab initio benchmark is obtained by exploring the PES using a hierarchical series of ab initio methods [HF, MP2, CCSD, CCSD(T)] in combination with a hierarchical series of five Gaussian-type basis sets, up to g polarization. Relativistic effects are taken into account either through a relativistic effective core potential for palladium or through a full four-component all-electron approach. Our best estimate of kinetic and thermodynamic parameters is -10.8 (-11.3) kcal/mol for the formation of the reactant complex, 19.4 (17.1) kcal/mol for the activation energy relative to the separate reactants, and -4.5 (-6.8) kcal/mol for the reaction energy (zero-point vibrational energy-corrected values in parentheses). Our work highlights the importance of sufficient higher angular momentum polarization functions for correctly describing metal-d-electron correlation. Best overall agreement with our ab initio benchmark is obtained by functionals from all three categories, GGA, meta-GGA, and hybrid DFT, with mean absolute errors of 1.5 to 2.5 kcal/mol and errors in activation energies ranging from -0.2 to -3.2 kcal/mol. Interestingly, the well-known BLYP functional compares very reasonably with a slight underestimation of the overall barrier by -0.9 kcal/mol. For comparison, with B3LYP we arrive at an overestimation of the overall barrier by 5.8 kcal/mol. On the other hand, B3LYP performs excellently for the central barrier (i.e., relative to the reactant complex) which it underestimates by only -0.1 kcal/mol. 相似文献
76.
In this article, we apply a novel time‐dependent discrete variable representation (TDDVR) method proposed by Barkakaty and Adhikari to investigate tunneling through an Eckart barrier. This semi‐classical method is theoretically rigorous and straightforward to implement. Among the TDDVR formulations, this report presents the first derivation of a rigorous form of quantum force (QF) for the present perspective. The validity of this semi‐classical approach is demanded based on the excellent agreement of the tunneling probability with the corresponding quantum results. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004 相似文献
77.
78.
We propose an algorithm for the computation ofL
1 (LAD) smoothing splines in the spacesW
M
(D), with
. We assume one is given data of the formy
i
=(f(t
i
) +
i
, i=1,...,N with {itti}
i=1
N D
, the
i
are errors withE(
i
)=0, andf is assumed to be inW
M
. The LAD smoothing spline, for fixed smoothing parameter0, is defined as the solution,s
, of the optimization problem
(1/N)
i=1
N
¦y
i
–g(t
i
¦+J
M
(g), whereJ
M
(g) is the seminorm consisting of the sum of the squaredL
2 norms of theMth partial derivatives ofg. Such an LAD smoothing spline,s
, would be expected to give robust smoothed estimates off in situations where the
i
are from a distribution with heavy tails. The solution to such a problem is a thin plate spline of known form. An algorithm for computings
is given which is based on considering a sequence of quadratic programming problems whose structure is guided by the optimality conditions for the above convex minimization problem, and which are solved readily, if a good initial point is available. The data driven selection of the smoothing parameter is achieved by minimizing aCV() score of the form
.The combined LAD-CV smoothing spline algorithm is a continuation scheme in 0 taken on the above SQPs parametrized in, with the optimal smoothing parameter taken to be that value of at which theCV() score first begins to increase. The feasibility of constructing the LAD-CV smoothing spline is illustrated by an application to a problem in environment data interpretation. 相似文献
79.
The selectivity of a column system, S, defined by equation 28, includes a variation coefficient (β) of plate number with capacity ratio which has a large influence on the peak capacity, as shown in Fig. 18. Some typical chromatograms are given. In order to predict S for a column system from Kovat's Index, equations 40 and 41 are given to calculate the constant of the carbon number rule for squalane at different temperatures or for different stationary phases. The specific retention value of heptane on squalane at different temperatures can be calculated from equation 42. The nonpolarity index, defined by equation 43, was used to calculate the retention value of heptane on various stationary phases. In liquid chromatography, the order of elution may be reversed by changing the composition of the eluent on the same chemically bonded silica (manufactured in China). The linear relations between the log retention values of different kinds of solutes or of a single solute on the silicas of different surface areas when using the same eluent are given. 相似文献
80.
The molecular structures and vibrational spectra of the three isomers of pyridinecarboxamide (picolinamide, nicotinamide, isonicotinamide) were calculated with the Density Functional Theory (DFT) method using the B3LYP function and the 6-31++G(d,p), Z2PolX, Z3PolX basis sets. The calculations were performed by using the Gaussian98W packet program set. The total energy distributions (TED) of the vibrational modes of these molecules were calculated by using the Scale 2.0 program and the vibrational modes of the molecules were determined. The Scaled Quantum Mechanical (SQM) method was used in the scaling procedure. In the experimental part of the study, the solid phase FT-IR and Micro Raman spectra of the three isomers of pyridinecarboxamide have been recorded in the range of 4000-650 and 1200-100 cm−1, respectively. The calculated wavenumbers were compared to the corresponding experimental values. As a result, the observed bands of the three isomers of pyridinecarboxamide were assigned with good accuracy. 相似文献