Desorption of n-alkanes from graphene: a van der Waals density functional study

A recent study of temperature programmed desorption (TPD) measurements of small n-alkanes (CNH2N+2) from C(0001) deposited on Pt(111) shows a linear relationship of the desorption energy with increasing n-alkane chain length. We here present a van der Waals density functional study of the desorption barrier energy of the ten smallest n-alkanes (N = 1 to 10) from graphene. We find linear scaling with N, including a nonzero intercept with the energy axis, i.e., an offset at the extrapolation to N = 0. This calculated offset is quantitatively similar to the results of the TPD measurements. From further calculations of the polyethylene polymer we offer a suggestion for the origin of the offset.Comment: 3 pictures, 1 tabl

A density functional for sparse matter

Sparse matter is abundant and has both strong local bonds and weak nonbonding forces, in particular nonlocal van der Waals (vdW) forces between atoms separated by empty space. It encompasses a broad spectrum of systems, like soft matter, adsorption systems and biostructures. Density-functional theory (DFT), long since proven successful for dense matter, seems now to have come to a point, where useful extensions to sparse matter are available. In particular, a functional form, vdW-DF (Dion et al 2004 Phys. Rev. Lett. 92 246401; Thonhauser et al 2007 Phys. Rev. B 76 125112), has been proposed for the nonlocal correlations between electrons and applied to various relevant molecules and materials, including to those layered systems like graphite, boron nitride and molybdenum sulfide, to dimers of benzene, polycyclic aromatic hydrocarbons (PAHs), doped benzene, cytosine and DNA base pairs, to nonbonding forces in molecules, to adsorbed molecules, like benzene, naphthalene, phenol and adenine on graphite, alumina and metals, to polymer and carbon nanotube (CNT) crystals, and hydrogen storage in graphite and metal–organic frameworks (MOFs), and to the structure of DNA and of DNA with intercalators. Comparison with results from wavefunction calculations for the smaller systems and with experimental data for the extended ones show the vdW-DF path to be promising. This could have great ramifications

Adsorption of dichlorobenzene on Au and Pt stepped surfaces using van der Waals density functional theory

The adsorption of dichlorobenzene on flat (111) and stepped (332) Au and Pt surfaces was studied using density functional theory with both a conventional generalized gradient approximation (GGA) and a fully nonlocal van der Waals density functional (vdW-DF). The equilibrium geometries and adsorption energies were computed for several different adsorption configurations. The two functionals yielded qualitatively different results, with the GGA functional predicting only weak binding compared to vdW-DF, demonstrating the importance of including nonlocal dispersion. By analyzing the electronic density and projected density of states, it was found that the interaction of dichlorobenzene with the two surfaces caused a charge redistribution, especially for the stepped surfaces. Moreover, adsorption on the step edge on Au(332) was dominated by nonlocal dispersion, whereas adsorption on the Pt(332) step was dominated by chemical bonding

RPBE-vdW Description of Benzene Adsorption on Au(111)

Density functional theory has become a popular methodology for the analysis of molecular adsorption on surfaces. Despite this popularity, there exist adsorption systems for which commonly used exchange-correlation functionals fail miserably. Particularly those systems where binding is due to van der Waals interactions. The adsorption of benzene on Au(111) is an often mentioned such system where standard density functionals predict a very weak adsorption or even a repulsion, whereas a significant adsorption is observed experimentally. We show that a considerable improvement in the description of the adsorption of benzene on Au(111) is obtained when using the so-called RPBE-vdW functional

Optical absorption spectrum of rotated trilayer graphene

Using ab initio calculations we have studied the optical linear response of different configurations of twisted trilayer graphene systems. We have found that when one of the outer layers is rotated the system shows an angle-dependent optical spectrum as its twisted bilayer counterpart; however, in this case there are two absorption peaks located in the visible range of the spectrum and one more in the intermediate infrared range for large relative rotation angles. When two layers are rotated the spectrum exhibits only two absorption peaks in the visible range revealing information about the two relative rotation angles between the layers in the structure. All these absorption peaks in the visible range shift to the intermediate infrared range for small angles