Nuclear Orbital Approach Research Articles

Unravelling Coriolis temperature-dependent effects on doped helium clusters: Vib-rotational Raman spectra of (3,4He)4–Cl2(X)

Coriolis effects, induced by the molecular rotation, on doped helium clusters are unravelled by calculating the vib-rotational Raman spectra of (3,4He)4–Cl2(X) clusters as a function of the temperature. Quantum Chemistry-like calculations using the Full-Configuration-Interaction Nuclear-Orbital approach reveal the key role of spin-dependent couplings in fermionic clusters at very low temperatures (0.07K) for the first time, signaling the effective decoupling of the spin angular momentum from the molecular rotation. On the other hand, the spectra of bosonic (spinless) (4He4)–Cl2 clusters are almost unperturbed by Coriolis couplings at the considered temperature range (1–0.37K).

Collective Bosonic Excitations in Doped para-H2 Clusters through the Full-Configuration-Interaction Nuclear Orbital Approach

The onset of collective rotational states as minima in the energy spectra of bosonic spin-less para-H2 (pH2) molecules confined in a belt around a molecular dopant is studied by analyzing excites states in (pH2)N-CO2 clusters (N ≤ 5). These minima result from a combined effect of a bosonic-symmetry-induced boundary periodic condition in cyclic arrangements of pH2 and the increasingly intensified hard-core of the effective pH2–pH2 interaction as N increases. The same also applies to doped 4He clusters in a contrast with the fermionic 3He case (N ≤ 4). The onset of the minima for pH2 and 4He marks a reversal in the apparent scaling of the rotational constant with N for the axial rotation around the dopant (from inversely proportional to proportional), whereas the 3He counterpart retains the regular dependence. The newly developed full-configuration-interaction nuclear orbital approach for bosons is presented here for the first time.

Microscopic description of small doped 3He clusters through the full‐configuration‐interaction nuclear orbital approach: The (3He)N‐Br2(X) case revisited

AbstractWe have completed our previous study on small (3He)N‐Br2(X) clusters (de Lara‐Castells et al., J Chem Phys (Communication) 2006, 125, 221101) by using larger one‐particle basis sets and an enhanced implementation of the full‐configuration‐ interaction nuclear orbital treatment to calculate ground and excited “solvent” states of small doped 3HeN clusters (de Lara‐Castells et al., J Chem Phys 2009, 131, 194101). Because of the inherent hard‐core interaction problem owing to the strong He–He repulsive potential at short distances, very large one‐particle basis sets are necessary to get converged results. Very similar results to those found for clusters with Cl2(B) as the dopant species have been found, owing more to the rather similar anisotropic T‐shaped character of the used He‐dopant potential energy surfaces than to the dominance of the He‐dopant attractive interaction over the He–He one in both cases. The results of the numerical testing by modifying the strength of the He–He potential interaction provide further evidences into the microscopic interactions holding the clusters together. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Quantum solvent states and rovibrational spectra of small doped H3e clusters through the full-configuration-interaction nuclear orbital approach: The (H3e)N–Cl2(X) case (N≤4)

A full-configuration-interaction nuclear orbital treatment has been recently developed as a benchmark quantum-chemistry-like method to study small doped (3)He clusters [M. P. de Lara-Castells et al., J. Chem. Phys. 125, 221101 (2006)]. Our objective in this paper is to extend our previous study on ((3)He)(N)-Cl(2)(B) clusters, using an enhanced implementation that allows employing very large one-particle basis sets [M. P. de Lara-Castells et al., J. Chem. Phys. 131, 194101 (2009)], and apply the method to the ((3)He)(N)-Cl(2)(X) case, using both a semiempirical T-shaped and an ab initio He-dopant potential with minima at both T-shaped and linear conformations. Calculations of the ground and low-lying excited solvent states stress the key role played by the anisotropy of the He-dopant interaction in determining the global energies and the structuring of the (3)He atoms around the dopant. Whereas (3)He atoms are localized in a broad belt around the molecular axis in ground-state N-sized complexes with N=1-3, irrespective of using the T-shaped or the ab initio He-dopant potential function, the dopant species becomes fully coated by just four (3)He atoms when the He-dopant potential also has a minimum at linear configurations. However, excited solvent states with a central ring-type clustering of the host molecule are found to be very close in energy with the ground state by using the ab initio potential function. A microscopic analysis of this behavior is provided. Additional simulations of the molecular rovibrational Raman spectra, also including excited solvent states, provide further insights into the importance of proper modeling the anisotropy of the He-dopant interaction in these weakly bound systems and of taking into account the low-lying excitations.

An optimized full-configuration-interaction nuclear orbital approach to a “hard-core” interaction problem: Application to (H3e)N–Cl2(B) clusters (N≤4)

An efficient full-configuration-interaction nuclear orbital treatment has been recently developed as a benchmark quantum-chemistry-like method to calculate ground and excited "solvent" energies and wave functions in small doped DeltaE(est) clusters (N < or = 4) [M. P. de Lara-Castells, G. Delgado-Barrio, P. Villarreal, and A. O. Mitrushchenkov, J. Chem. Phys. 125, 221101 (2006)]. Additional methodological and computational details of the implementation, which uses an iterative Jacobi-Davidson diagonalization algorithm to properly address the inherent "hard-core" He-He interaction problem, are described here. The convergence of total energies, average pair He-He interaction energies, and relevant one- and two-body properties upon increasing the angular part of the one-particle basis set (expanded in spherical harmonics) has been analyzed, considering Cl(2) as the dopant and a semiempirical model (T-shaped) He-Cl(2)(B) potential. Converged results are used to analyze global energetic and structural aspects as well as the configuration makeup of the wave functions, associated with the ground and low-lying "solvent" excited states. Our study reveals that besides the fermionic nature of (3)He atoms, key roles in determining total binding energies and wave-function structures are played by the strong repulsive core of the He-He potential as well as its very weak attractive region, the most stable arrangement somehow departing from the one of N He atoms equally spaced on equatorial "ring" around the dopant. The present results for N = 4 fermions indicates the structural "pairing" of two (3)He atoms at opposite sides on a broad "belt" around the dopant, executing a sort of asymmetric umbrella motion. This pairing is a compromise between maximizing the (3)He-(3)He and the He-dopant attractions, and suppressing at the same time the "hard-core" repulsion. Although the He-He attractive interaction is rather weak, its contribution to the total energy is found to scale as a power of three and it thus increasingly affects the pair density distributions as the cluster grows in size.