Research Article  Open Access
Sherin A. Saraireh, Mohammednoor Altarawneh, "Electronic Structure of the CuCl_{2}(100) Surface: A DFT FirstPrinciple Study", Journal of Nanomaterials, vol. 2012, Article ID 767128, 7 pages, 2012. https://doi.org/10.1155/2012/767128
Electronic Structure of the CuCl_{2}(100) Surface: A DFT FirstPrinciple Study
Abstract
Firstprinciple density functional theory (DFT) and a periodicslab model have been utilized to investigate the structure of the CuCl_{2}(100) surface. Structural parameters of the bulk CuCl_{2} are reported and compared with the experimental values. The structure of the CuCl_{2}(100) is calculated using a () supercell. Structural parameters in terms of bond lengths and bond angle are calculated. Electronic properties of the CuCl_{2}(100) surface are investigated by calculating the density of state (DOS) and the projected density of state for a slab containing five layers.
1. Introduction
Copper plays a prominent role in many fields. This is primarily due to its unique mechanical properties and excellent electrical and thermal conductivity. Its applications spans heating and cooling piping, heat exchanging, electrical appliances, architecture, and catalysis [1–6].
Adsorption of halides on metallic surfaces is of particular importance due to their relevance for many industrial processes and its role in the formation of notorious environmental pollutants such as dioxins [7]. Central to a comprehensive understanding of various phenomena such as corrosion, electrodeposition, and catalytic cycles is addressing adsorption of chlorine on copper surfaces on a precise atomicscale.
Motivated by its diverse application, the chlorinecopper interaction has attracted great deal of experimental [8–14] and theoretical [15–18] studies. Mounting experimental evidence shows a strong interaction between Cl and Cu atoms as evident from electron diffraction (LEED) [8], normalincident Xray standing wave (NIXSW) [9], surfaceextended Xray adsorption fine structure (SEXAFS) [10, 11], shadowconeenhanced secondaryion mass spectrometry (SIMS) [6, 12], and Scanning Tunnelling microscopy (STM) [13, 14] methods. STM studies found that the chlorine molecules adsorb dissociatively on the Cu(111) surface, leading to formation of various wellordered phases. It is also found that Cl atoms prefer to adsorbs onto facecentered cubic (fcc) hollow positions over the hexagonal closepack (hcp) hollow, bridge, and top positions [13, 18].
Computational data for the Cl/Cu(111) system based on cluster [15] or a periodic DFTbased calculation [16, 17, 19] has been presented by different groups Doll and Harrison [16], Migani et al. [17], and Peljhan and Kokalj [19]. It was found that the preferred adsorption of the Cl atoms is the facecentered cubic (fcc) [16]. Peljhan et al. presented an extensive DFT calculation of Cl adsorption on Cu(111), considering a wide range of Cl coverages ranging from 1/16 to 1 ML. The strong interaction between Cl and Cu atoms results in the formation of two distinctive different materials; namely, CuCl and CuCl_{2}. The crystal structure of the CuCl_{2} follows a basecentered monoclinic space group C2/m [20–22]. As demonstrated by Burns and Hawthrone [23]. Cu atoms are positioned in an axially distorted octahedral environment with four equatorial nearest neighbors Cl atoms and two axial Cu atoms.
Firstprinciple simulation, based on density functional theory (DFT), is now one of the key tools for studying and developing a key understanding of solid surfaces. DFT calculations can provide an atomicbased insight into the detailed bonding arrangement of structures, their energetic stability, and charge densities. To this end, this contribution investigates the electronic structure of the Copper (II) chloride, CuCl_{2}, mainly in the (100) surface orientation.
2. Methodology
The calculations reported in this paper have been performed using the plane wave pseudopotential density functional theory (DFT) method as implemented in the VASP program [24–27]. The generalized gradient approximation (GGA) for exchange and correlation as developed by Perdew and Wang (PW91) [28] was used to perform the spinpolarized calculations. Projector augmented wave (PAW) potentials [24, 25, 29] are used to represent the ionic potentials. A unit cell comprising four atomic layers has been employed together with a vacuum thickness of at least 14 Å to separate each slab from its neighboring images along the direction (normal to the surface). The three topmost layers of the slab were allowed to fully relax. The BrillouinZone (BZ) integrations were performed using automatic generation of (3 × 3 × 1) and (5 × 5 × 1) point set of MonkhorstPack random sampling [30]. Total energy was converged to an accuracy of 1 × 10^{−3} eV. Deployed energy cutoff was set at 300 eV. The choice of this value, stems from the maximum value of the kineticenergy for the Cl and Cu atoms, that is, 280 and 273 eV, respectively.
3. Results
3.1. Bulk Properties
CuCl_{2} forms a basecentered Monoclinic Bravies lattice. As shown in Figure 1, each Cu atom is in an axially distorted octahedral environment with four equatorial nearest neighbors Cl atoms and two axial Cl atoms. The lattice constants were determined (as illustrated in Table 1) by plotting the variation in the energy with respect to the volume of the unit cell of bulk CuCl_{2}. The lattice constants of bulk CuCl_{2} are compared with calculated data in reference [19] and experiment data in references [23, 31] in Table 1. This comparison shows that our results are in a relative good agreement with those of earlier experiment and computational studies.
The calculated total density of states (DOS) and atomicprojected DOS (pDOS) for bulk CuCl_{2} are presented in Figure 2; Figure 2(a) shows the Density of state (DOS) of the CuCl_{2} bulk, while Figure 2(b) shows the projected density of state for Cu atom and Figure 2(c) shows the projected density of state for Cl atom.
(a)
(b)
(c)
There are two distinct bands in the valence region (Figure 2(a)). The Cu band (predominantly Cu 3d and little contributions of Cu (3p and 4s)) occupies the region (0 to −5) eV, and the Cl band (predominantly Cl (3s and 3p)) occupies that of (−14 to −15) eV. The surface state band resides just above the Fermi level where two regions are highlighted. The first one is in the region from 3.0 to 7.0 eV, while the second one is from 7.5 to 9.0 eV. The first region above the Fermi level is predominantly the empty state Cu 4s and the contribution in this region from Cu 3p and Cl (3s and 3p) is minimal (see Figures 2(b) and 2(c)). The second region above the Fermi level is predominantly the state Cu (3d and 3p) and Cl (3s and 3p).
3.2. CuCl_{2}(100) Surface
A supercell of the CuCl_{2}(100) is constructed from the optimized bulk unitcell and also based on the data in [21, 22, 32]; the unit cell is shown in Figure 3. This unit cell is a basecentered Monoclinic with one Cu atom located in the center of each base and four Cl atoms in the corner of each base. The Cu atom has four nearest neighbors Cl atoms in the same plane (plane of a and b) and two Cl atoms in c direction.
Test is performed using automatic generation of (3 × 3 × 1) and (5 × 5 × 1) point set of Monkhorst and Pack. For each optimization using these two schemes, the total energy was converged to an accuracy of 1 × 10^{−3} eV and the forces on each ion to an accuracy of 0.015 eV Å^{−1}. A test using (5 × 5 × 1) point changed the total energies of the (3 × 3 × 1) point by a only few meV. All the calculations discussed here are using a 3 × 3 × 1 point grid (unless otherwise specified).
Transformation upon building the surface can be viewed in terms of the relaxation, that is, the change in interatomic distances and angle between optimized bulk unit cell and the extended surface. We found that CuCl distances become longer in the extended surface than the bulk one by only 0.009 Å. While the angle on the unit cell unit cell varies between 117° in the bulk and 111.3° in the surface (as shown in Figure 3). It is worthwhile also mentioning that optimized surface retains the symmetry exhibited by the unit cell. A noticeable difference in and lattice constants could be rationalized based on the shortcoming of standard DFT methods in descrying states relating to longterm weak interactions (Van der Walls type) [33, 34].
The surface has a space group C2/m (as shown in Figure 3) the same as that of the CuCl_{2} bulk. Unit cells are shifted from each other by 4.06 Å. The supercell of the surface is illustrated in Figure 4; the top and side views are also shown in Figure 5. All bond lengths and bond angles are illustrated in Table 2 based on Figure 5(b). The distance between each two atomic layer is 3.212 Å. The surface has been optimized also by the (5 × 5 × 5) point set, and some of the bond lengths and bond angles are illustrated also in Table 2 based on Figure 5(b). As can be noticed from Table 2, some of the bond length shrinks slightly by 0.02 Å while the others stay the same. Also some of the bond angle did not change, while the others changed by only 0.2°. Angle in the unit cell illustrated in Figure 3 becomes smaller also by 0.8°.

(a)
(b)
(a)
(b)
3.3. Electronics Properties
The electronics properties of the CuCl_{2}(100) surface are investigated by calculating the density of state (DOS) for a slab containing five layers using the automatic generation of (3 × 3 × 1) point. Figure 6 shows the total DOS and projected DOS of the surface. The investigation of the DOS shows that there are three main regions in the valence band below the Fermi level (0 eV in Figure 6(a)). The first and second regions occupy the regions of (−2 to −6) eV and (−6 to −8) eV. These two regions are manly composed of Cu 3d (Figure 6(b)), with a little contribution of Cl 3p, but the Cu (4s and 3p) and Cl 3s states are minimal (Figures 6(b) and 6(c)).
(a)
(b)
(c)
The last region in the valence band is starting at −17 eV; it is composed of Cl 3s states. The conduction band has two distinct regions starting at 1.5 eV with a wide of approximately 2.5 eV for each one. Each of these regions has small peaks at 3.2 eV and 5.2 eV, respectively. The first region is predominantly Cu (4s and 3p) and Cl (3s and 3p), while the second region is predominantly of Cu 4s and the Cl (3s and 3p).
4. Conclusions
The structural, electronic properties of bulk and (100) surface of CuCl_{2} were investigated by means of periodic quantum chemical calculation based on the firstprinciple DFT approach. For the bulk, the comparison of optimized structural parameters with experimental and previous DFT study shows that the lattice constants are in a good agreement. The supercell of the CuCl_{2}(100) surface showed to be axially distorted in the direction. The interlayer distance, all the bond lengths, and the bond angle are calculated.
Total and projected Density of State (DOS) for the bulk and the extended surface is calculated. For the (100) surface, the valence band is having two regions: the first one composed of Cu (3d) and Cl (3p), while the second region is composed of Cl (3s) states. The surface states above the Fermi level are composed of manly Cu (4s and 3p) and Cl (3s and 3p). An extension to this work is to study the adsorption and dissociation of small molecules such as H_{2} and H_{2}O on this surface.
References
 K. S. Subramanian, “Determination of tin in lead/tin solder leachates from copper piping by graphite platform furnace atomicabsorption spectrometry,” Talanta, vol. 36, no. 11, pp. 1075–1080, 1989. View at: Google Scholar
 V. V. Smirnov and J. P. Roth, “Mechanisms of electron transfer in catalysis by copper zinc superoxide dismutase,” Journal of the American Chemical Society, vol. 128, no. 51, pp. 16424–16425, 2006. View at: Publisher Site  Google Scholar
 W. F. Paxton, J. M. Spruell, and J. F. Stoddart, “Heterogeneous catalysis of a coppercoated atomic force microscopy tip for directwrite click chemistry,” Journal of the American Chemical Society, vol. 131, no. 19, pp. 6692–6694, 2009. View at: Publisher Site  Google Scholar
 J. Song, T. Zhao, and Y. Du, “Supported copper catalysts for direct vaporphase oxycarbonylation of methanol,” Chinese Journal of Catalysis, vol. 27, no. 5, pp. 386–390, 2006. View at: Publisher Site  Google Scholar
 Y. Cen, X. Li, and H. Liu, “Preparation of copperbased catalysts for methanol synthesis by acidalkalibased alternate precipitation method,” Chinese Journal of Catalysis, vol. 27, no. 3, pp. 210–216, 2006. View at: Publisher Site  Google Scholar
 M. H. Looi, S. T. Lee, and S. B. AbdHamid, “Use of citric acid in synthesizing a highly dispersed copper catalyst for selective hydrogenolysis,” Chinese Journal of Catalysis, vol. 29, no. 6, pp. 566–570, 2008. View at: Publisher Site  Google Scholar
 M. Altarawneh, B. Z. Dlugogorski, E. M. Kennedy, and J. C. Mackie, “Mechanisms for formation, chlorination, dechlorination and destruction of polychlorinated dibenzopdioxins and dibenzofurans (PCDD/Fs),” Progress in Energy and Combustion Science, vol. 35, no. 3, pp. 245–274, 2009. View at: Publisher Site  Google Scholar
 P. J. Goddard and R. M. Lambert, “Adsorptiondesorption properties and surface structural chemistry of chlorine on Cu(111) and Ag(111),” Surface Science, vol. 67, no. 1, pp. 180–194, 1977. View at: Google Scholar
 M. F. Kadodwala, A. A. Davis, G. Scragg et al., “Structural determination of the Cu(111)($3\times 3$) R30°Cl/Br surface using the normal incidence XRay standing wave method,” Surface Science, vol. 324, no. 23, pp. 122–132, 1995. View at: Google Scholar
 M. D. Crapper, C. E. Riley, P. J. J. Sweeney, C. F. McConville, and D. P. Woodruff, “Complete adsorption site information for Cl on Cu(111) using Xray absorption fine structure and photoelectron diffraction,” EPL (Europhysics Letters), vol. 2, no. 11, p. 857, 1986. View at: Publisher Site  Google Scholar
 D. P. Woodruff, D. L. Seymour, C. F. McConville et al., “Simple xray standingwave technique and its application to the investigation of the Cu(111) (√3 √3) R30°Cl structure,” Physical Review Letters, vol. 58, no. 14, pp. 1460–1462, 1987. View at: Publisher Site  Google Scholar
 W. K. Way, A. C. Pike, S. W. Rosencrance, R. M. Braun, and N. Winograd, “Coveragedependent bond length of chlorine adsorbed on Cu(111),” Surface and Interface Analysis, vol. 24, no. 2, pp. 137–141, 1996. View at: Google Scholar
 T. Sakurai and T. Hashizume, “FISTM study of metal surfaces,” Nanotechnology, vol. 3, no. 3, pp. 126–132, 1992. View at: Publisher Site  Google Scholar
 D. W. Suggs and A. J. Bard, “Scanning tunneling microscopic study with atomic resolution of the dissolution of Cu(111) in aqueous chloride solutions,” Journal of the American Chemical Society, vol. 116, no. 23, pp. 10725–10733, 1994. View at: Publisher Site  Google Scholar
 A. Ignaczak and J. A. Gomes, “Interaction of halide ions with copper: the DFT approach,” Chemical Physics Letters, vol. 257, no. 56, pp. 609–615, 1996. View at: Publisher Site  Google Scholar
 K. Doll and N. M. Harrison, “Chlorine adsorption on the Cu(111) surface,” Chemical Physics Letters, vol. 317, no. 3–5, pp. 282–289, 2000. View at: Publisher Site  Google Scholar
 A. Migani, C. Sousa, and F. Illas, “Chemisorption of atomic chlorine on metal surfaces and the interpretation of the induced work function changes,” Surface Science, vol. 574, no. 23, pp. 297–305, 2005. View at: Publisher Site  Google Scholar
 A. Migani and F. Illas, “A systematic study of the structure and bonding of halogens on lowindex transition metal surfaces,” Journal of Physical Chemistry B, vol. 110, no. 24, pp. 11894–11906, 2006. View at: Publisher Site  Google Scholar
 S. Peljhan and A. Kokalj, “Adsorption of Chlorine on Cu(111): A Density Functional Theory Study,” The Journal of Physical Chemistry C, vol. 113, no. 32, pp. 14363–14376, 2009. View at: Publisher Site  Google Scholar
 L. B. Bergasova and S. K. Filatov, “The new mineral tolbachite CuCl_{2},” Doklady Akademii Nauk SSSR, vol. 270, pp. 415–417, 1983. View at: Google Scholar
 B. Gmelin, Handbuch Der Aanorganischen Chemie, vol. 211, Chemie GmbH, Weinheim, Germany, 1958.
 A. F. Wells, “333. The crystal structure of anhydrous cupric chloride, and the stereochemistry of the cupric atom,” Journal of the Chemical Society, vol. 1, pp. 1670–1675, 1947. View at: Publisher Site  Google Scholar
 P. C. Burns and F. C. Hawthrone, “Tolbachite, CuCl_{2}, the first example of Cu^{2+} octahedrally coordinated by Cl^{},” The American Mineralogist, vol. 78, pp. 187–189, 1993. View at: Google Scholar
 G. Kresse and J. Hafner, “Ab initio molecular dynamics for liquid metals,” Physical Review B, vol. 47, no. 1, pp. 558–561, 1993. View at: Publisher Site  Google Scholar
 G. Kresse and J. Hafner, “Ab initio moleculardynamics simulation of the liquidmetal–amorphoussemiconductor transition in germanium,” Physical Review B, vol. 49, no. 20, pp. 14251–14269, 1994. View at: Publisher Site  Google Scholar
 G. Kresse and J. Furthmuller, “Efficiency of abinitio total energy calculations for metals and semiconductors using a planewave basis set,” Computational Materials Science, vol. 6, no. 1, pp. 15–50, 1996. View at: Publisher Site  Google Scholar
 G. Kresse and J. Furthmuller, “Efficient iterative schemes for ab initio totalenergy calculations using a planewave basis set,” Physical Review B, vol. 54, no. 16, pp. 11169–11186, 1996. View at: Publisher Site  Google Scholar
 J. P. Perdew, J. A. Chevary, S. H. Vosko et al., “Atoms, molecules, solids, and surfaces: applications of the generalized gradient approximation for exchange and correlation,” Physical Review B, vol. 46, no. 11, pp. 6671–6687, 1992. View at: Publisher Site  Google Scholar
 P. E. Blöchl, “Projector augmentedwave method,” Physical Review B, vol. 50, no. 24, pp. 17953–17979, 1994. View at: Publisher Site  Google Scholar
 H. J. Monkhorst and J. D. Pack, “Special points for Brillouinzone integrations,” Physical Review B, vol. 13, no. 12, pp. 5188–5192, 1976. View at: Publisher Site  Google Scholar
 D. R. Lide, Ed., CRC Handbook of Chemistry and Physics, CRC Press, Boca Raton, Fla, USA, 7th edition, 1993.
 J. Find, D. Herein, Y. Uchida, and R. Schlögl, “New threedimensional structural model for the CuCl_{2} graphite intercalation compound,” Carbon, vol. 37, no. 9, pp. 1431–1441, 1999. View at: Publisher Site  Google Scholar
 M. Altarawneh, M. W. Radny, P. V. Smith, J. C. Mackie, E. M. Kennedy, and B. Z. Dlugogorski, “2Chlorophenol adsorption on Cu(1 0 0): firstprinciples density functional study,” Surface Science, vol. 602, no. 8, pp. 1554–1562, 2008. View at: Publisher Site  Google Scholar
 O. A. Lilienfeld, I. Tavernelli, U. Rothlisberger, and D. Sebastiani, “Optimization of effective atom centered potentials for London dispersion forces in density functional theory,” Physical Review Letters, vol. 93, no. 15, Article ID 153004, 2004. View at: Publisher Site  Google Scholar
Copyright
Copyright © 2012 Sherin A. Saraireh and Mohammednoor Altarawneh. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.