Parallel computing for 4-atomic molecular dynamics calculations

The Journal of Chemical Physics, 2011

We report quantum dynamics calculations of rotational and vibrational energy transfer in collisions between two para-H 2 molecules over collision energies spanning from the ultracold limit to thermal energies. Results obtained using a recent full-dimensional H 2 -H 2 potential energy surface (PES) developed by Hinde [J. Chem. Phys. 128, 154308 (2008)] are compared with those derived from the Boothroyd, Martin, Keogh, and Peterson (BMKP) PES [J. Chem. Phys. 116, 666 ]. For vibrational relaxation of H 2 (v = 1, j = 0) by collisions with H 2 (v = 0, j = 0) as well as rotational excitations in collisions between ground state H 2 molecules, the PES of Hinde is found to yield results in better agreement with available experimental data. A highly efficient near-resonant energy transfer mechanism that conserves internal rotational angular momentum and was identified in our previous study of the H 2 -H 2 system [Phys. Rev. A 77, 030704(R) (2008)] using the BMKP PES is also found to be reproduced by the Hinde PES, demonstrating that the process is largely insensitive to the details of the PES. In the absence of the near-resonance mechanism, vibrational relaxation is driven by the anisotropy of the potential energy surface. Based on a comparison of results obtained using the Hinde and BMKP PESs with available experimental data, it appears that the Hinde PES provides a more accurate description of rotational and vibrational transitions in H 2 -H 2 collisions, at least for vibrational quantum numbers v ≤ 1.

Journal of Physics B: Atomic, Molecular and Optical Physics, 2020

We present benchmark integrated and differential cross-sections for electron collisions with H2 using two different theoretical approaches, namely, the R-matrix and molecular convergent close-coupling. This is similar to comparative studies conducted on electron–atom collisions for H, He and Mg. Electron impact excitation to the b 3 Σ u + , a 3 Σ g + , B 1 Σ u + , c3Πu, E F 1 Σ g + , C1Πu, e 3 Σ u + , h 3 Σ g + , B ′ 1 Σ u + and d3Πu excited electronic states are considered. Calculations are presented in both the fixed nuclei and adiabatic nuclei approximations, where the latter is shown only for the b 3 Σ u + state. Good agreement is found for all transitions presented. Where available, we compare with existing experimental and recommended data.

Chemical Physics, 1995

Partially decoupled quantum mechanical calculations, termed VCC-RIOS in the main text, which occur in the H 2 molecule colliding with protons are carried out for the vibrational excitation processes. A broad range of collision energies, up to 70 eV, is examined and results are compared with existing data for average energy transfer, integral cross sections and differential cross sections. A very detailed comparison with various experiments is carried out at E = 20 eV and satisfactory agreement with both experiments and earlier calculations is found for several dynamical observables. Through the present, extensive study of the higher energy behaviour of cross sections it is possible to further test the quality of one of the existing PES and to confirm the mode of behaviour for the charge-transfer channels that open up as the molecule becomes vibrationally 'hot' during collisions. * Corresponding author. Fax: +39-6-49913305. E.mail:

Journal of Computational Chemistry, 2006

A new parallel algorithm has been developed for second-order Møller-Plesset perturbation theory (MP2) energy calculations. Its main projected applications are for large molecules, for instance, for the calculation of dispersion interaction. Tests on a moderate number of processors (2-16) show that the program has high CPU and parallel efficiency. Timings are presented for two relatively large molecules, taxol (C 47 H 51 NO 14) and luciferin (C 11 H 8 N 2 O 3 S 2), the former with the 6-31G* and 6-311G** basis sets (1032 and 1484 basis functions, 164 correlated orbitals), and the latter with the aug-cc-pVDZ and aug-cc-pVTZ basis sets (530 and 1198 basis functions, 46 correlated orbitals). An MP2 energy calculation on C 130 H 10 (1970 basis functions, 265 correlated orbitals) completed in less than 2 h on 128 processors.

High Performance Computing in Science and Engineering ‘14, 2014

Petaflop architectures are currently being utilized efficiently to perform large scale computations in Atomic, Molecular and Optical Collisions. We solve the Schrödinger or Dirac equation for the appropriate collision problem using the R-matrix or R-matrix with pseudo-states approach. We briefly outline the parallel methodology used and implemented for the current suite of Breit-Pauli and DARC codes. In this report, various examples are shown of our theoretical results compared with experimental results obtained from Synchrotron Radiation facilities where the Cray architecture at HLRS is playing an integral part in our computational projects.

The Journal of Chemical Physics, 2014

Collision-induced energy transfer involving H 2 molecules plays an important role in many areas of physics. Kinetic models often require a complete set of state-to-state rate coefficients for H 2 +H 2 collisions in order to interpret results from spectroscopic observations or to make quantitative predictions. Recent progress in full-dimensional quantum dynamics using the numerically exact closecoupling (CC) formulation has provided good agreement with existing experimental data for lowlying states of H 2 and increased the number of state-to-state cross sections that may be reliably determined over a broad range of energies. Nevertheless, there exist many possible initial states (e.g., states with high rotational excitation) that still remain elusive from a computational standpoint even at relatively low collision energies. In these cases, the coupled-states (CS) approximation offers an alternative full-dimensional formulation. We assess the accuracy of the CS approximation for H 2 +H 2 collisions by comparison with benchmark results obtained using the CC formulation. The results are used to provide insight into the orientation effects of the various internal energy transfer mechanisms. A statistical CS approximation is also investigated and cross sections are reported for transitions which would otherwise be impractical to compute. © 2014 AIP Publishing LLC. [http://dx.

The Journal of Chemical Physics, 1991

The Darakjian-Hayes direct method for determining quantum lifetimes for three atoms scattering in three physical dimensions is used to determine accurate state-to-state time delays for the reaction of helium with H,+ for total angular momentum J = 0. These results are compared with the time delays obtained by numerical differentiation of the S-matrix elements generated using the APH (adiabatically adjusting principal-axis hyperspherical) formulation of Pack and Parker. The direct method was found to be accurate and efficient for calculating the energy derivatives of the S matrix. The calculated eigenvalues of Smith's collision lifetime matrix (eigen lifetimes) for this reaction predict numerous long-lived metastable states, many with lifetimes over 0.5 ps. The extent of the coupling of metastable states to specific scattering states provides an indication of the nature and magnitude of the time delays associated with particular state-to-state scattering processes. The direct method for calculating the energy derivatives of the S matrix is also found to be accurate and efficient for determining the energy derivative of the cumulative reaction probability. 2516 J. Chem. Phys. 95 (4),

Physical Review A, 2002

We present a detailed quantum-mechanical study for dissociation of vibrationally excited molecular diatomic target, of H 2 ( i ) by proton impact and H 2 ϩ ( i ) by hydrogen-atom impact, in the range of center-of-mass collision energies from threshold to 9.5 eV. The dominant dissociation mechanisms in this three-atomic collision system are identified and their effectiveness analyzed for different collision geometries. The cross section calculations for direct and charge-transfer dissociation are performed by solving the Schrödinger equation for the nuclear and electronic motions on the two lowest diabatic electronic surfaces of H 3 ϩ , and by using an expansion of nuclear wave function in a vibrational basis containing all discrete H 2 and H 2 ϩ states and a large number of pseudostates from each of the corresponding discretized continua. The energy and angular spectra of the fragments are also calculated and analyzed.

Chemical Physics, 1991

The Darakjian-Hayes direct method for determining quantum lifetimes for three atoms scattering in three physical dimensions is used to determine accurate state-to-state time delays for the reaction of helium with H,+ for total angular momentum J = 0. These results are compared with the time delays obtained by numerical differentiation of the S-matrix elements generated using the APH (adiabatically adjusting principal-axis hyperspherical) formulation of Pack and Parker. The direct method was found to be accurate and efficient for calculating the energy derivatives of the S matrix. The calculated eigenvalues of Smith's collision lifetime matrix (eigen lifetimes) for this reaction predict numerous long-lived metastable states, many with lifetimes over 0.5 ps. The extent of the coupling of metastable states to specific scattering states provides an indication of the nature and magnitude of the time delays associated with particular state-to-state scattering processes. The direct method for calculating the energy derivatives of the S matrix is also found to be accurate and efficient for determining the energy derivative of the cumulative reaction probability. 2516 J. Chem. Phys. 95 (4),

1991

The Darakjian-Hayes direct method for determining quantum lifetimes for three atoms scattering in three physical dimensions is used to determine accurate state-to-state time delays for the reaction of helium with H,+ for total angular momentum J = 0. These results are compared with the time delays obtained by numerical differentiation of the S-matrix elements generated using the APH (adiabatically adjusting principal-axis hyperspherical) formulation of Pack and Parker. The direct method was found to be accurate and efficient for calculating the energy derivatives of the S matrix. The calculated eigenvalues of Smith's collision lifetime matrix (eigen lifetimes) for this reaction predict numerous long-lived metastable states, many with lifetimes over 0.5 ps. The extent of the coupling of metastable states to specific scattering states provides an indication of the nature and magnitude of the time delays associated with particular state-to-state scattering processes. The direct method for calculating the energy derivatives of the S matrix is also found to be accurate and efficient for determining the energy derivative of the cumulative reaction probability. 2516 J. Chem. Phys. 95 (4),