A density functional and quantum Monte Carlo study of glutamic acid in vacuo and in a dielectric continuum medium

2012 ◽  
Vol 137 (7) ◽  
pp. 075102 ◽  
Author(s):  
Franca Maria Floris ◽  
Claudia Filippi ◽  
Claudio Amovilli
Keyword(s):  
Monte Carlo ◽  
Glutamic Acid ◽  
Quantum Monte Carlo ◽  
Density Functional ◽  
Monte Carlo Study ◽  
Dielectric Continuum

scholarly journals Quantum Monte Carlo Study of Silicon Self-interstitial Defects

VLSI Design ◽  
2001 ◽  
Vol 13 (1-4) ◽  
pp. 229-235 ◽  
Author(s):  
W.-K. Leung ◽  
R. J. Needs ◽  
G. Rajagopal ◽  
S. Itoh ◽  
S. Ihara
Keyword(s):  
Monte Carlo ◽  
Quantum Monte Carlo ◽  
Density Functional ◽  
Monte Carlo Study ◽  
Functional Theory ◽  
Self Diffusion ◽  
A Value ◽  
Interstitial Defects ◽  
Quantum Monte Carlo Methods ◽  
And Diffusion

We give a brief description of the variational and diffusion quantum Monte Carlo methods and their application to the study of self-interstitial defects in silicon. The diffusion quantum Monte Carlo calculations give formation energies for the most stable defects of about 4.9 eV, which is considerably larger than the values obtained in density functional theory methods. The quantum Monte Carlo results indicate a value for the formation+migration energy of the self-interstitial contribution to self-diffusion of about 5 eV, which is consistent with the experimental data.

Quantum Monte Carlo Study of Water Molecule: A Preliminary Investigation

2004 ◽  
Vol 57 (12) ◽  
pp. 1229 ◽  
Author(s):  
Nicole A. Benedek ◽  
Irene Yarovsky ◽  
Kay Latham ◽  
Ian K. Snook
Keyword(s):  
Monte Carlo ◽  
Water Molecule ◽  
Quantum Monte Carlo ◽  
Density Functional ◽  
Correlation Energy ◽  
Preliminary Investigation ◽  
Monte Carlo Study ◽  
System Size ◽  
Basis Sets ◽  
Advantages And Disadvantages

The Quantum Monte Carlo (QMC) technique[1] offers advantages of good scaling with system size (number of electrons) and an ability to uniformly recover over 90% of the electron correlation energy, compared to the more conventional quantum chemistry approaches. For the water molecule in its ground state, it has been shown[2] that the QMC method gives results that are comparable in accuracy to those obtained by the best available conventional methods, while at the same time using much more modest basis sets than is necessary with these methods. Furthermore, the effect of the orbitals needed for these QMC calculations (which may be obtained from either Hartree–Fock or Density Functional Theory) has been investigated. Both the advantages and disadvantages of the QMC method are discussed.

scholarly journals Non-Covalent Forces in Naphthazarin—Cooperativity or Competition in the Light of Theoretical Approaches

2021 ◽  
Vol 22 (15) ◽  
pp. 8033
Author(s):  
Aneta Jezierska ◽  
Kacper Błaziak ◽  
Sebastian Klahm ◽  
Arne Lüchow ◽  
Jarosław J. Panek
Keyword(s):  
Monte Carlo ◽  
Perturbation Theory ◽  
Potential Energy ◽  
Proton Transfer ◽  
Ir Spectra ◽  
Quantum Monte Carlo ◽  
Density Functional ◽  
Theoretical Approaches ◽  
Study Results ◽  
Intramolecular Hydrogen

Non-covalent interactions responsible for molecular features and self-assembly in Naphthazarin C polymorph were investigated on the basis of diverse theoretical approaches: Density Functional Theory (DFT), Diffusion Quantum Monte Carlo (DQMC), Symmetry-Adapted Perturbation Theory (SAPT) and Car-Parrinello Molecular Dynamics (CPMD). The proton reaction paths in the intramolecular hydrogen bridges were studied. Two potential energy minima were found indicating that the proton transfer phenomena occur in the electronic ground state. Diffusion Quantum Monte Carlo (DQMC) and other levels of theory including Coupled Cluster (CC) employment enabled an accurate inspection of Potential Energy Surface (PES) and revealed the energy barrier for the proton transfer. The structure and reactivity evolution associated with the proton transfer were investigated using Harmonic Oscillator Model of Aromaticity - HOMA index, Fukui functions and Atoms In Molecules (AIM) theory. The energy partitioning in the studied dimers was carried out based on Symmetry-Adapted Perturbation Theory (SAPT) indicating that dispersive forces are dominant in the structure stabilization. The CPMD simulations were performed at 60 K and 300 K in vacuo and in the crystalline phase. The temperature influence on the bridged protons dynamics was studied and showed that the proton transfer phenomena were not observed at 60 K, but the frequent events were noticed at 300 K in both studied phases. The spectroscopic signatures derived from the CPMD were computed using Fourier transformation of autocorrelation function of atomic velocity for the whole molecule and bridged protons. The computed gas-phase IR spectra showed two regions with OH absorption that covers frequencies from 2500 cm−1 to 2800 cm−1 at 60 K and from 2350 cm−1 to 3250 cm−1 at 300 K for both bridged protons. In comparison, the solid state computed IR spectra revealed the environmental influence on the vibrational features. For each of them absorption regions were found between 2700–3100 cm−1 and 2400–2850 cm−1 at 60 K and 2300–3300 cm−1 and 2300–3200 cm−1 at 300 K respectively. Therefore, the CPMD study results indicated that there is a cooperation of intramolecular hydrogen bonds in Naphthazarin molecule.

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