Robust wave function optimization procedures in quantum Monte Carlo methods

Self Cite

We present a quantum Monte Carlo study of the solvation and spectroscopic properties of the Mg doped helium clusters MgHen with n = 2 − 50. Three high level (MP4, CCSD(T) and CCSDT) MgHe interaction potentials have been used to study the sensitivity of the dopant location on the shape of the pair interaction. Despite the similar MgHe well depth, the pair distribution functions obtained in the diffusion Monte Carlo simulations markedly differ for the three pair potentials, therefore indicating different solubility properties for Mg in Hen. Moreover, we found interesting size effects for the behavior of the Mg impurity.As a sensitive probe of the solvation properties, the Mg excitation spectra have been simulated for various cluster sizes and compared with the available experimental results. The interaction between the excited 1 P Mg atom and the He moiety has been approximated using the Diatomics-in-Molecules method and the two excited 1 Π and 1 Σ MgHe potentials. The shape of the simulated MgHe50 spectra show a substantial dependency on the location of the Mg impurity, and hence on the MgHe pair interaction employed.To unravel the dependency of the solvation behavior on the shape of the computed potentials, exact Density Functional Theory has been adapted to the case of doped Hen and various energy distributions have been computed. The results indicate the shape of the repulsive part of the MgHe potential as an important cause of the different behaviours.

“…[37]. The optimized wave functions were successively employed to guide the DMC simulations of the doped clusters in order to sample the mixed distribution f (R) = Φ 0 (R)Ψ T (R).…”

Section: Methodsmentioning

confidence: 99%

Predicting atomic dopant solvation in helium clusters: The MgHen case

Mella

Calderoni

Cargnoni

2005

Self Cite

“…We first optimize the trial wavefunction using Variational Monte Carlo (VMC) (see for example ref. [30] for a general discussion and ref. [31] for the specific implementation).…”

Section: The Monte Carlo Calculationsmentioning

confidence: 99%

Bosonic helium droplets with cationic impurities: Onset of electrostriction and snowball effects from quantum calculations

Coccia

Bodo

Marinetti

et al. 2007

Variational MonteCarlo and Diffusion MonteCarlo calculations have been carried out for cations like Li + , Na + and K + as dopants of small helium clusters over a range of cluster sizes up to about 12 solvent atoms.The interaction has been modelled through a sum-of-potential picture that disregards higher order effects beyond atom-atom and atom-ion contributions. The latter were obtained from highly correlated ab-initio calculations over a broad range of interatomic distances.This study focuses on two of the most striking features of the microsolvation in a quantum solvent of a cationic dopant: electrostriction and snowball effects. They are here discussed in detail and in relation with the nanoscopic properties of the interaction forces at play within a fully quantum picture of the clusters features.

“…40 The present DMC implementation includes a tenth function to satisfy the electron-nucleus cusp condition. The optimization of correlation function parameters is accomplished through fixed sample optimization using the absolute deviation (AD) functional 41,42 that minimizes the energy of Ψ T and is given by,…”

Section: Qmc Methodologymentioning

confidence: 99%

Geometry optimization in quantum Monte Carlo with solution mapping: Application to formaldehyde

Schuetz

Frenklach

Kollias

et al. 2003

The solution mapping methodology is presented as a method of geometry optimization of molecules in the quantum Monte Carlo method. Applied to formaldehyde as a test system, this approach is found to yield optimized bond lengths and bond angle in the diffusion Monte Carlo method that lie within experimental error. The variational Monte Carlo optimized geometry also lies within experimental error, with the exception of the CH bond length, which is slightly underestimated. Additionally, the resulting quadratic representation of the potential energy surface in the region of the minimum is used to calculate three of the force constants and harmonic frequencies.2