scholarly journals Diffusion and Reptation Quantum Monte Carlo Study of the NaK Molecule

2018 ◽  
Author(s):  
Marc E. Segovia ◽  
Oscar Ventura
Keyword(s):  
Monte Carlo ◽  
Dipole Moment ◽  
Potential Energy ◽  
Dissociation Energy ◽  
Quantum Monte Carlo ◽  
Density Functional ◽  
Basis Set ◽  
Energy Curve ◽  
Dft Methods ◽  
Trial Wavefunction

<p>Diffusion Monte Carlo (DMC) and Reptation Monte Carlo (RMC) methods, have been applied to study some properties of the NaK molecule. Hartree-Fock (HF), Density Functional (DFT) and single and double configuration interaction (SDCI) wavefunctions with a valence quadruple zeta atomic natural orbital (VQZ/ANO) basis set were used as trial wavefunctions. Values for the potential energy curve, dissociation energy and dipole moment were calculated for all methods and compared with experimental results and previous theoretical derivations. Quantum Monte Carlo (QMC) calculations were shown to be useful methods to recover correlation in NaK, essential to obtain a reasonable description of the molecule. The equilibrium distance—interpolated from the potential energy curves—yield a value of 3.5 Å, in agreement with the experimental value. The dissociation energy, however, is not as good. In this case, a conventional CCSD(T) calculation with an extended aug-pc-4 basis set gives a much better agreement to experiment. On the contrary, the CCSD(T), other MO and DFT methods are not able to reproduce correctly the large dipole moment of this molecule. Even DMC methods with a simple HF trial wavefunction are able to give a better agreement to experiment. RMC methods are even better, and the value obtained with a B3LYP trial wavefunction is very close to the experimental one.</p>

Diffusion and Reptation Quantum Monte Carlo Study of the NaK Molecule

2018 ◽  
Author(s):  
Marc E. Segovia ◽  
Oscar Ventura
Keyword(s):  
Monte Carlo ◽  
Dipole Moment ◽  
Potential Energy ◽  
Dissociation Energy ◽  
Quantum Monte Carlo ◽  
Density Functional ◽  
Basis Set ◽  
Energy Curve ◽  
Dft Methods ◽  
Trial Wavefunction

<p>Diffusion Monte Carlo (DMC) and Reptation Monte Carlo (RMC) methods, have been applied to study some properties of the NaK molecule. Hartree-Fock (HF), Density Functional (DFT) and single and double configuration interaction (SDCI) wavefunctions with a valence quadruple zeta atomic natural orbital (VQZ/ANO) basis set were used as trial wavefunctions. Values for the potential energy curve, dissociation energy and dipole moment were calculated for all methods and compared with experimental results and previous theoretical derivations. Quantum Monte Carlo (QMC) calculations were shown to be useful methods to recover correlation in NaK, essential to obtain a reasonable description of the molecule. The equilibrium distance—interpolated from the potential energy curves—yield a value of 3.5 Å, in agreement with the experimental value. The dissociation energy, however, is not as good. In this case, a conventional CCSD(T) calculation with an extended aug-pc-4 basis set gives a much better agreement to experiment. On the contrary, the CCSD(T), other MO and DFT methods are not able to reproduce correctly the large dipole moment of this molecule. Even DMC methods with a simple HF trial wavefunction are able to give a better agreement to experiment. RMC methods are even better, and the value obtained with a B3LYP trial wavefunction is very close to the experimental one.</p>

Diffusion and Reptation Quantum Monte Carlo Study of the NaK Molecule

2018 ◽  
Author(s):  
Marc E. Segovia ◽  
Oscar Ventura
Keyword(s):  
Monte Carlo ◽  
Dipole Moment ◽  
Potential Energy ◽  
Dissociation Energy ◽  
Quantum Monte Carlo ◽  
Density Functional ◽  
Basis Set ◽  
Energy Curve ◽  
Dft Methods ◽  
Trial Wavefunction

<p>Diffusion Monte Carlo (DMC) and Reptation Monte Carlo (RMC) methods, have been applied to study some properties of the NaK molecule. Hartree-Fock (HF), Density Functional (DFT) and single and double configuration interaction (SDCI) wavefunctions with a valence quadruple zeta atomic natural orbital (VQZ/ANO) basis set were used as trial wavefunctions. Values for the potential energy curve, dissociation energy and dipole moment were calculated for all methods and compared with experimental results and previous theoretical derivations. Quantum Monte Carlo (QMC) calculations were shown to be useful methods to recover correlation in NaK, essential to obtain a reasonable description of the molecule. The equilibrium distance—interpolated from the potential energy curves—yield a value of 3.5 Å, in agreement with the experimental value. The dissociation energy, however, is not as good. In this case, a conventional CCSD(T) calculation with an extended aug-pc-4 basis set gives a much better agreement to experiment. On the contrary, the CCSD(T), other MO and DFT methods are not able to reproduce correctly the large dipole moment of this molecule. Even DMC methods with a simple HF trial wavefunction are able to give a better agreement to experiment. RMC methods are even better, and the value obtained with a B3LYP trial wavefunction is very close to the experimental one.</p>

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.

Quantum Monte Carlo with density matrix: potential energy curve derived properties

2017 ◽  
Vol 23 (4) ◽  
Author(s):  
Víctor S. Bonfim ◽  
Nádia M. Borges ◽  
João B. L. Martins ◽  
Ricardo Gargano ◽  
José Roberto dos S. Politi
Keyword(s):  
Monte Carlo ◽  
Potential Energy ◽  
Density Matrix ◽  
Quantum Monte Carlo ◽  
Potential Energy Curve ◽  
Energy Curve ◽  
Matrix Potential ◽  
Derived Properties

scholarly journals Quantum Monte Carlo calculated potential energy curve for the helium dimer

2010 ◽  
Vol 132 (20) ◽  
pp. 204304 ◽  
Author(s):  
Xuebin Wu ◽  
Xianru Hu ◽  
Yunchuan Dai ◽  
Chenlei Du ◽  
Shibin Chu ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Potential Energy ◽  
Quantum Monte Carlo ◽  
Potential Energy Curve ◽  
Energy Curve ◽  
Calculated Potential Energy

On the performance of density functional theory methods in the prediction of the electric polarizability and hyperpolarizability of ozone

2005 ◽  
Vol 1 (1) ◽  
pp. 31-36 ◽  
Author(s):  
George Maroulis
Keyword(s):  
Density Functional Theory ◽  
Dipole Moment ◽  
Ab Initio ◽  
Density Functional ◽  
Basis Set ◽  
Dft Methods ◽  
Functional Theory ◽  
Electric Polarizability ◽  
Rigorous Approach ◽  
High Level

We report a study of the performance of density functional theory (DFT) methods in the prediction of electric properties for the ozone molecule. We have used a large, flexible basis set for the calculation of the dipole moment and the dipole (hyper)polarizability with the B1LYP, B3LYP, B3P86, B3PW91, G96PW91 and MPW91PW91 methods. The results are compared to high-level, conventional ab initiomethods. We rely on a rigorous approach in order to evaluate the proximity and similarity of theoretical descriptions obtained via DFT and conventional ab initiomethods. We find that compared to the most accurate ab initio, DFT methods predict reliable dipole polarizabilities and second dipole hyperpolarizabilities for ozone. Agreement is less good for the dipole moment and the first dipole hyperpolarizability. Overall, the performance of the DFT is similar to that of the accurate ab initiomethods.

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