Pier Luigi Silvestrelli

STRUCTURAL, ELECTRONIC, AND BONDING PROPERTIES OF LIQUID WATER FROM FIRST PRINCIPLES

We study, from first principles, structural, electronic, and bonding properties of liquid water. Our system is twice as large as that used in previous ab initio simulations and our computed structural properties are in good agreement with the most recent neutron scattering experiments. Moreover, the use of a novel technique, based on the generation of maximally localized Wannier functions, allowed us to describe the molecular charge distribution and the polarization effects in liquid water with a degree of accuracy not previously possible. We find that, in the liquid phase, the water molecule dipole moment has a broad distribution around an average value of about 3.0 D. This value is 60% higher than that of the gas phase and significantly larger than most previous estimates. A considerable increase is also observed in the magnitude of the average eigenvalues of the quadrupole moment tensor. We also find that the anisotropy of the electronic charge distribution of the water molecule is reduced in the liqui...

AB INITIO INFRARED SPECTRUM OF LIQUID WATER

Abstract An ab initio calculation of the infrared spectrum of liquid water has been performed using Car-Parrinello molecular dynamics and evaluating the electronic polarization by means of the Berry phase formulation. The major features of the spectrum are in good agreement with experiments and are shown to arise from specific vibrational motions of the water molecules. The effect of quantum corrections to the spectrum is discussed.

Maximally-localized Wannier functions for disordered systems: Application to amorphous silicon

We use the maximally-localized Wannier function method to study bonding properties in amorphous silicon. This study represents, to our knowledge, the first application of the Wannier-function analysis to a disordered system. Our results show that, in the presence of disorder, this method is extremely helpful in providing an unambiguous picture of the bond distribution. In particular, defect configurations can be studied and characterized with a novel degree of accuracy that was not available before.

Van der Waals Interactions in DFT Made Easy by Wannier Functions

Ubiquitous van der Waals interactions between atoms and molecules are important for many molecular and solid structures. These systems are often studied from first principles using the density functional theory (DFT). However, the commonly used DFT functionals fail to capture the essence of van der Waals effects. Most attempts to correct for this problem have a basic semiempirical character, although computationally more expensive first principles schemes have been recently developed. We here describe a novel approach, based on the use of the maximally localized Wannier functions, that appears to be promising, being simple, efficient, accurate, and transferable (charge polarization effects are naturally included). The results of test applications to small molecules and bulk graphite are presented.

van der Waals Interactions in Density Functional Theory Using Wannier Functions

van der Waals interactions between atoms and molecules are ubiquitous and very important for many molecular and condensed-matter structures. These systems are often studied from first principles using the density functional theory (DFT), because this approach often represents a good compromise between accuracy and efficiency. However, the commonly used DFT functionals are not able to describe properly van der Waals effects. Most attempts to correct for this problem have a basic semiempirical character, although computationally more expensive first principles schemes have been recently developed. Of course, the key issue is finding a way to include van der Waals interactions in DFT without dramatically increasing the computational cost. We here describe in detail the recently developed scheme, based on the use of the maximally localized Wannier functions, that combines the simplicity of the semiempirical formalism with the accuracy of the first principles approaches and appears to be promising, being simple, efficient, accurate, and transferable (for instance, charge polarization effects are naturally included). The results of successful applications to small molecules, bulk Ar, and the interaction of Ar, He, and H(2) with two different Al surfaces are presented. Directions for further improvements of the method are finally suggested.

Adsorption of benzene on Si(100) from first principles

Adsorption of benzene on the Si(100) surface is studied from first principles. We find that the most stable configuration is a tetra-

Physisorption, Diffusion, and Chemisorption Pathways of H2 Molecule on Graphene and on (2,2) Carbon Nanotube by First Principles Calculations.

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Compton scattering and the character of the hydrogen bond in ice Ih

-bonded structure characterized by one C-C double bond and four C-Si bonds. A similar structure, obtained by rotating the benzene molecule by 90 degrees, lies slightly higher in energy. However, rather narrow wells on the potential energy surface characterize these adsorption configurations. A benzene molecule impinging on the Si surface is most likely to be adsorbed in one of three different di-

Ab initio molecular dynamics simulation of laser melting of graphite

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Van der Waals interactions at surfaces by density functional theory using Wannier functions

-bonded, metastable structures, characterized by two C-Si bonds, and eventually converts into the lowest-energy configurations. These results are consistent with recent experiments.