Radiation-induced Cationic Polymerization of Butadiene

Several stochastic simulations of the TIP4P ͓W. L. Jorgensen, J. Chandrasekhar, J. D. Madura, R. W. Impey, and M. L. Klein, J. Chem. Phys. 79, 926 ͑1983͔͒ water octamer are performed. Use is made of the stereographic projection path integral and the Green's function stereographic projection diffusion Monte Carlo techniques, recently developed in one of our groups. The importance sampling for the diffusion Monte Carlo algorithm is obtained by optimizing a simple wave function using variational Monte Carlo enhanced with parallel tempering to overcome quasiergodicity problems. The quantum heat capacity of the TIP4P octamer contains a pronounced melting peak at 160 K, about 50 K lower than the classical melting peak. The zero point energy of the TIP4P water octamer is 0.0348Ϯ 0.0002 hartree. By characterizing several large samples of configurations visited by both guided and unguided diffusion walks, we determine that both the TIP4P and the SPC ͓H. J. C. Berendsen, J. P. Postma, W. F. von Gunsteren, and J. Hermans, ͑Intermolecular Forces, Reidel, 1981͒. p. 331͔ octamer have a ground state wave functions predominantly contained within the D 2d basin of attraction. This result contrasts with the structure of the global minimum for the TIP4P potential, which is an S 4 cube. Comparisons of the thermodynamic and ground-state properties are made with the SPC octamer as well.

Section: Introductionmentioning

confidence: 99%

The thermodynamic and ground state properties of the TIP4P water octamer

Asare

Musah

Curotto

et al. 2009

“…Originally developed by Anderson,20,21 the DMC method exploits the fact that the time-dependent Schrödinger equation for the imaginary time = it is analogous to the diffusion equation with an additional source/sink term, and can therefore be solved by a random walk. Detailed descriptions of the DMC method are available in the literature.…”

Section: B Diffusion Monte Carlo Calculations Of Ground-state Energimentioning

confidence: 99%

Ar n HF van der Waals clusters revisited: II. Energetics and HF vibrational frequency shifts from diffusion Monte Carlo calculations on additive and nonadditive potential-energy surfaces for n=1-12

Jiang

Hutson

et al. 2005

The ground-state energies and HF vibrational frequency shifts of ArnHF clusters have been calculated on the nonadditive potential-energy surfaces (PESs) for n=2-7 and on the pairwise-additive PESs for the clusters with n=1-12, using the diffusion Monte Carlo (DMC) method. For n>3, the calculations have been performed for the lowest-energy isomer and several higher-lying isomers which are the closest in energy. They provide information about the isomer dependence of the HF redshift, and enable direct comparison with the experimental data recently obtained in helium nanodroplets. The agreement between theory and experiment is excellent, in particular, for the nonadditive DMC redshifts. The relative, incremental redshifts are reproduced accurately even at the lower level of theory, i.e., the DMC and quantum five-dimensional (rigid Arn) calculations on the pairwise-additive PESs. The nonadditive interactions make a significant contribution to the frequency shift, on the order of 10%–12%, and have to be included in the PESs in order for the theory to yield accurate magnitude of the HF redshift. The energy gaps between the DMC ground states of the cluster isomers are very different from the energy separation of their respective minima on the PES, due to the considerable variations in the intermolecular zero-point energy of different ArnHF isomers.

“…24 In this approach, each of the molecular units in a complex is treated as a rigid rotor, and we propagate the center of mass and the rotational motion of each of these molecular units. In the present work, the diffusion of the centers of mass is implemented using standard DMC techniques, [22][23][24][25] and the rotational diffusion is implemented by propagating the rotation matrices that define the orientation of the principal axes of each molecular unit relative to the space-fixed reference frame. 18…”

Section: A Diffusion Monte Carlo "Dmc…mentioning

confidence: 99%

“…Several methods have been suggested to address this issue. 25,[30][31][32][33] In this work we employ a variant of the fixed node approximation that was originally proposed by Anderson,22,23,25,34 and allow the node to be slowly varied throughout the simulation. 18,26 The basic idea behind this method is identical to the algorithm used in the evaluation of expectation values.…”

Section: Excited Vibrational Statementioning

confidence: 99%

“…40 In the calculations of the energies of the three excited bending states, the -bend, which corresponds to rotation of Ne 2 and the in-plane and out-of-plane bends of OH/D, the locations of the nodal surfaces are determined by symmetry. Therefore, the usual fixed node approximation 22,23,25,34 is employed for calculations that involve these states. In the case of the remaining two states, which are totally symmetric, the location of the nodal surfaces and corresponding energies are determined by ADMC.…”

Section: B Excited Vibrational States Of Ne 2 Ohõdmentioning

confidence: 99%

See 1 more Smart Citation

Quantum Monte Carlo studies of the structure and spectroscopy of NenOH (Ã 2Σ+, n=1–4) van der Waals complexes

Lee

McCoy

2001

Adiabatic rigid-body diffusion Monte Carlo is used to study the structure and spectroscopy of complexes of OH(Ã 2Σ+) with several neon atoms. Although the potential energy surfaces for these systems have many low-lying minima, the ground state wave functions are localized in the global minimum. This trend is found to persist in the first few vibrationally excited states of Ne2OH/D. Low-lying vibrational states that are localized in the potential minimum that corresponds to the linear Ne–OH/D–Ne configuration of the complex are also found.