Phenol-Modified Silicene: Preferred Substitution Site and Electronic

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Phenol-Modified Silicene; Preferred Substitution site and Electronic Properties Michael R. Bassett, Tetsuya Morishita, Hugh Frederick Wilson, Amanda S. Barnard, and Michelle Jeanette Sapountzis Spencer J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b09914 • Publication Date (Web): 22 Jan 2016 Downloaded from http://pubs.acs.org on January 27, 2016

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The Journal of Physical Chemistry

Phenol-modified Silicene; Preferred Substitution Site and Electronic Properties Michael R. Bassett,† Tetsuya Morishita,*‡ Hugh F. Wilson,†¶ Amanda S. Barnard,¶ and Michelle J. S. Spencer*†¶ †

School of Science, RMIT University, GPO Box 2476 Melbourne, Victoria 3001, Australia

‡

Nanomaterials Research Institute (NRI), National Institute of Advanced Industrial Science and

Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan ¶

Manufacturing Flagship, CSIRO, 343 Royal Parade, Parkville, Victoria 3052, Australia

ACS Paragon Plus Environment

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ABSTRACT: Silicon nanosheets (or multilayer silicene) are one of the most exciting recent discoveries, being a two-dimensional form of silicon that is less than a nanometer thick, with large lateral dimensions. It has been shown previously that organo-modified silicene can be synthesised with phenyl groups covalently bonded to both sides of the nanosheet, with hydrogen atoms terminating the under-coordinated silicon atoms [J. Am. Chem. Soc., 2010, 132 59465947; Phys. Chem. Chem. Phys., 2011, 13 15418–22]. In this work, we use density-functional theory calculations and ab initio molecular dynamics simulations to determine the effect of hydroxyl (OH) group substitution on the phenyl-modified silicene. We show that van der Waals forces need to be included in the simulation to represent the interactions between the groups on the nanosheet. Different positions of the OH groups on the phenyl rings were modelled including ortho-, meta- and para- substituted positions. The para-substituted position was favoured, followed by the metathen ortho- substituted positions. Our ab initio MD simulations showed that the phenol groups will freely rotate on the nanosheet, aligning so as to form hydrogen bonds between adjacent phenol groups. Such a property may allow the material to be soluble in aqueous solutions, extending its application areas.

KEYWORDS: density functional theory, silicon, silicene, nanosheet, nanomaterial, phenol, functionalization, phenyl, surface termination.


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INTRODUCTION The unique properties observed in nanomaterials, in comparison to their bulk counterparts, continues to prompt widespread and in-depth research into the nature of such materials and how these properties can be manipulated to yield revolutionary applications. One category of nanomaterials that shows no signs of slowing is that of the two-dimensional (2D) nanosheet.1 The discovery of graphene has led to much exciting research, however, in recent years attention has turned to similar structures in elements such as silicon. Silicene has risen to prominence as an exciting analogue of graphene. Similarly structured, as a single layer of silicon atoms, this new crystalline form of silicon has progressed from theoretical models to reality in a matter of years, with silicene being grown deposited on a variety of substrates,2-6 as well as functionalised with different organic groups (see Okamoto et al.7 and Wang et al.8,9 and references therein). Silicene offers strong candidacy for electronic device and sensing applications and is expected to address performance and scalability limitations presented by its bulk counterpart. Given the conventional use of silicon in the semiconductor industry, and the enormous global investment in this domain, this area is a primary research focus. Theoretical10-13 and experimental7,14,15 studies of silicene and thicker nanosheets have led to the successful synthesis of unmodified and modified forms of the material via chemical vapour deposition (CVD) and organic synthesis approaches. The latter approach has yielded functionalised silicene with a variety of surface modifications. Of particular interest here are the phenyl (-C6H5) modified silicene sheets synthesised by Sugiyama et al.16 These nanostructures comprise a single layer silicene sheet, terminated on both surfaces with phenyl groups and hydrogen atoms. Confirmation of the structure was carried out by characterisation with IR and 1H-NMR spectroscopy, X-ray absorption near-edge structure (XANES), photoluminescence


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spectroscopy, atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques.16 The likely orientation and structure of these adsorbed phenyl groups were investigated using forcefield calculations16 and subsequently with density-functional theory (DFT) calculations to confirm the proposed structure of this phenyl-modified silicene.17 The latter showed that phenyl groups were covalently bonded to the sheet, retaining the tetrahedral geometry observed in the unmodified silicene. The nanosheet was determined to be semiconducting, possessing a wide direct band gap of 1.92 eV. More recent DFT calculations by Spencer et al.18 investigated the nature of the interaction between the phenyl-modified silicene sheets when stacked on top of one another. As the interactions between the layers is likely to be weak,19 a comparison of the adhesion energy curves for a range of van der Waals (vdW) density functionals20-22 and the DFTD2 Grimme method23 highlighted the importance of accounting for vdW forces at close separations. At large separations, however, the structure and properties of the nanosheet were modelled equally well with both vdW- and non-vdW DFT methods. This may be fortuitous, and is worthy of further scrutiny. In order to extend the applications of chemically-modifed silicene, other functional groups need to be considered. The extent to which the band gap can be altered is an example of one important question. The question of the solubility of the nanomaterial, which is important for applications where ‘wet’ environments are required, is another. The phenyl-modified silicene has already been shown to be soluble in organic solutions; if the functional groups can be altered so that the material is soluble in aqueous solutions, then the applications of this material could be extended. Preliminary DFT calculations have been used to investigate the effect of hydroxyl (OH) substitution of one of the hydrogen atoms on the phenyl groups, i.e. phenol (-C6H5OH) modified


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silicene.24 This work used the DFT-PBE functional to model the ortho-, meta- and parasubstitutional sites, however the impact of vdW forces was omitted. In this work we examine the effect of using the vdW-DFT and DFT-D2 methods on the structure and properties of phenolmodified silicene. We predict the preferred substitution site of the hydroxyl group (ortho-, metaor para-) and determine the resulting electronic properties. We also use the density-functionalbased tight binding (DFTB) method to investigate phenol-modified nanosheets with larger lateral dimensions. As we will show, the incorporation of hydrophilic groups on the nanosheet structure yields new property changes and facilitates expansion of the potential applications of these materials.

COMPUTATIONAL METHODS The calculations were performed within the framework of DFT using the projector-augmented wave method25 and the generalized-gradient approximation using three different functionals: the exchange correlation functional of Perdew, Burke, and Ernzerhof (PBE),26 the DFT-D2 method of Grimme23 and a vdW-DF functional of Langreth and Lundqvist et al. (specifically the optB88vdW exchange functional)20-22 as implemented in the Vienna ab initio simulation package.27-29 We specifically chose the optB88 functional as this gave us good agreement with experimentally synthesized nanomaterial14 for modeling the interactions between the phenyl-modified silicene.17 The electronic wave functions were expanded in a plane-wave basis with an energy cut-off of 400 eV. A k-point mesh of 8×8×1, including the Γ point, was employed to sample the Brillouin zone (BZ). The organomodified Si nanosheet was constructed using the phenyl-modified Si nanosheet that has been synthesized and modelled previously.16-17 This nanosheet has 2 phenyl groups above and 2 phenyl groups below the nanosheet and was modified by substituting one of the H atoms


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on each phenyl group with an OH group. We specifically chose this surface loading as it corresponds to the surface loading that has already been achieved experimentally for phenylmodified silicene.16 We believe that using a coverage that is most likely to exist in reality gives our chosen structures greater validity than modelling other coverages that may be impossible to produce experimentally. Three different substitutional sites were modelled, with the OH groups substituted in the ortho, meta or para positions. During the geometry optimisation the lattice parameters were fixed while the atomic positions were relaxed until the total energy was converged to 10-4 eV and the Hellmann-Feynman force on each relaxed atom was less than 0.01 eV/Å. Each structure was initially optimized, followed by an ab initio MD simulation (as implemented in VASP) at 300 K, using a plane wave basis set expanded at the Γ point only in the Brillouin zone. The MD was performed for up to 10 ps, using a time step of 0.5 fs. A geometry optimisation was performed after 2.5 ps or 10 ps, with the most stable of these structures presented below. A series of calculations were also performed within the framework of DFTB on the same cells. Tight binding calculations were performed using the DFTB+ code30-31 using parameters from the matsci-0-3 set. Long-range vdW interactions were (optionally) added using a Lennard Jones form using parameters from the Universal Force Field (UFF).32 Geometries were optimised starting from stable DFT geometries, then subjected to twenty thousand molecular dynamics timesteps of 0.5 fs at 300 K or 600 K, then re-optimised. Larger structures were also modeled with DFTB, using [2x2] cells and the same procedure (geometry optimisation followed by 10 ps MD and then a further geometry optimization on the final structure), in order to determine whether a larger supercell would allow different longer-ranged structures to appear. A 4x4 kpoint grid was used for the [2 x 2] supercell.


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The Bader partial charges were calculated according to the procedure described by Henkelman et al.33 We found that a denser FFT grid (by a factor of up to 2) was necessary to achieve convergence.

RESULTS & DISCUSSION Relative stability The relative energy values of the ortho-, meta- and para- substituted phenol-modified silicene structures calculated using the different DFT functionals are shown in Table 1. When using the PBE functional, the meta-substituted structure is most stable, followed by the para- and then ortho- systems.24 However, when vdW forces are included in the calculation, using the optB88vdW functional and DFT-D2 method of Grimme, the order of stability changes. For both these methods, the para-substituted system is calculated to be the most stable, followed by the metathen ortho- substituted systems. When we consider what the geometry of these structures looks like (in the next section) we will discuss why vdW corrections should be included when modelling this system. In order to determine whether increasing the dimensions of the nanosheet could alter the orientation and possibly relative stability of the attached phenol groups, we performed DFTB calculations on the three substituted systems. The calculations showed that the meta-substituted system is most stable, followed by the para- and then ortho- substituted systems. We note, however, that the difference between the meta- and para- systems is < 0.04 eV/supercell, which is within the uncertainty of the DFTB energy, so is not inconsistent with the DFT-vdW findings. As the structure of each of the systems (Figure S2) was also almost identical to those obtained using the DFT calculations, we believe that the DFTB method is valid for examining nanosheets with larger lateral dimensions. We therefore used the DFTB to model supercells that were four times larger than those shown in Figure 1 (that is [2x2] cells), and


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computationally prohibitive using the DFT methods. These calculations showed that the order of stability remained the same as for the smaller [1x1] cells (see Table 1) even showing a smaller energy difference of 0.02 eV/unit cell between the para- and meta- substituted systems. The geometry of the 3 systems was also almost identical with the smaller supercells, indicating that the structure obtained in the smaller cells is the same when the periodic boundary conditions are increased in size, thereby validating the feasibility of using the smaller systems to represent the phenol-modified silicene.

Table 1. Relative total energy (relative stability) in eV of the different phenol-modified silicene structures using different density-functional-based methods. Relative energy (eV) Position

DFT

DFT-D2

vdW-DFT

DFTB DFTB

(PBE) (Grimme)

(optB88)

(no vdWs)

ortho

+0.32

+0.21

+0.32

+0.480

+0.511

meta

0.00

+0.11

+0.06

0.00

0.00

para

+0.12

0.00

0.00

+0.036

+0.016

Structure The relaxed phenol-modified silicene structures, calculated using the optB88 vdW-DFT functional are shown in Fig. 1. The corresponding structures calculated with the Grimme method are very similar, so are presented in Supplementary data (Figure S1). The structures of the orthoand metasystems are similar to those determined using the PBE functional (i.e. no inclusion of van der Waals),24 however, there are significant changes in the orientation of the phenol groups for the para-substituted system (Figure 1c) compared to Figure 1d)). For this latter system


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(Figure 1c)), the phenol groups have tilted on the sheet so that they lean towards each other to allow the OH groups on adjacent phenol groups to sit closer to each other. This is indicative of a hydrogen-type bonding interaction, and results in channels or rows of tilted phenol groups along the nanosheet. The geometry of the phenol groups is found to be the same above and below the

Figure 1. Structure of the relaxed monolayer organosilicon nanosheet showing side (top) and top (bottom) views with the OH groups in the (a) ortho- (b) meta- and (c) para-substituted positions, calculated with vdW-DFT using the optB88 functional; (d) para- substituted structure calculated with DFT-PBE functional. (Si, C, H and O atoms shown in yellow, grey, white and red, respectively).


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silicene sheet; however, the groups tilt in different directions so as to create an asymmetry above and below the sheet. This overall tilting of the groups results in a small buckling of the silicene where the H atoms attached to the sheet tilt away from the perpendicular, to reduce steric overlap with the phenol groups. It is known that the structure of isolated phenol dimers is dependent on the interplay between hydrogen bonding interactions between the hydroxyl groups and by dispersion interactions between the aromatic rings.32 For our structures, as the phenol groups are tethered to the silicon nanosheet at a separation distance of >6 Å, the hydrogen bonding will play a more important role in the final orientation of the phenol groups. The calculated values for the closest distance of the hydrogen type bonds (as measured between O-H•••O or H•••O-H) and the OH•••O or H•••OH angle are presented in Table 2 for all three substituted systems. For the ortho- and metasystems, the values are within ~0.1 Å whether vdW forces are included (vdW-DFT-optB88, and DFT-D2 Grimme) or not included (DFT-PBE). For the para-substituted phenol-modified silicene, however, the distances are up to 4 Å shorter when vdW forces are included, consistent with the structures presented visually in Figure 1. The OH•••H distances and angles for the groups above and below the sheet are close to the experimental values in a phenol dimer of 2.354 Å and 150.6°, respectively34 confirming the presence of hydrogen bonds. An electron localization function (ELF) plot of the meta- and parasubstituted phenol-modified silicene (using optB88) is presented in Figure 2. A slice through neighbouring phenol groups shows an increased probability of electron localization (measured from 0 to 1) between the H atom of one OH group and the O atom of an adjacent phenol group, further supporting the presence of hydrogen-type bonding interactions between adjacent phenol groups.


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Figure 2. Electron localisation function plots of (a) meta- and (b) para-substituted phenolmodified silicene, calculated using vdW-DFT with the optB88 functional. The slice passes through the O and H atoms of the phenol group on the left and the O atom of the phenol group on the right. (Red/blue regions represent high/low electron localization).

Using the optB88 functional, the distance between the hydrogen bond acceptor and donor is only 0.45 Å shorter (0.21 Å for DFTB) for the groups on the underside of the silicene sheet than on the top. This asymmetry is due to the dynamic motion of the groups on the nanosheet where they are seen to rotate and tilt at different angles during the MD simulation. At some point in the simulation, the phenol groups on the top of the sheet would align themselves closer together, however, the structure presented here shows substitution of hydroxyl groups on the phenyl rings induces hydrogen bonding interactions. Overall, the phenol groups attached to the sheet are oriented so that the hydrogen bonding is maximized. For the meta- and ortho- substituted systems, the groups remain oriented almost vertical on the sheet, but rotate about the z-axis so that the OH groups on adjacent rings lie next to each other; favouring any hydrogen-type bonding between the groups. Again, the calculated bond lengths


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and angles are indicative of the formation of hydrogen bonds but the angle tends to be smaller, indicating a weaker bond. For all systems, the phenol groups orient themselves in such a manner that maximal interaction between adjacent OH groups is achieved, i.e. each phenol group interacts with two other OH groups. For the DFTB-vdW calculated structures (Figure S2), inclusion of vdW forces results in shorter H-bond distances and smaller angles for all three structures (see Table 2), consistent with the DFT calculations.

Table 2. Calculated distances and angles between the OH groups on the phenol-modified structures using different density-functional-based methods. The shortest distances or largest angles for each interaction of the phenol groups above and below the silicene sheet are presented.

Position

ortho meta para

Position

ortho meta para

Calculated distances (Å) and angles (°) between OH groups DFT DFT-D2 vdW-DFT (optB88) (PBE) (Grimme) d < d < d < 2.00 137 2.05 133 2.02 136 1.99 137 1.94 137 1.94 141 1.91 158 3.04 103 3.01 104 2.98 118 1.84 158 1.83 161 6.25 152 2.36 153 2.47 155 4.97 159 2.97 163 2.02 164 Calculated distances (Å) and angles (°) between OH groups DFTB DFTB DFTB (no vdW) [2x2] cell d < d < d < 3.51 104 2.08 117 3.51 104 2.08 117 3.30 97.4 2.28 121 2.78 114 3.42 119 4.20 122 3.38 113 3.29 128 5.84 142 3.28 128 3.08 155 5.74 145 3.08 155


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The calculated values for the DFTB-vdW structures are slightly larger than for the opt-B88 and Grimme structures indicating that this method may slightly underestimate the H-bonding interaction. This difference may also result in the similarity in stability for the para- and metasystems. Of significant importance is the similarity in the calculated values for the larger supercells compared to the smaller ones (see Figure S3), indicating that the size of the supercell is not constraining the orientation of the molecules on the silicene surface.

Electronic Properties The distribution of charge in each of the phenol-modified silicene sheets was determined by calculating the Bader partial charges on different regions of the structures using the vdW-DF optB88 method. These charges are shown in Table 3 and it can be seen that unlike the phenylmodified structure,17-18 the presence of the OH groups has drawn much of the electron density away from the nanosheet and into the functional groups.

Table 3. Calculated partial charges on different regions of the phenol-modified silicene structures using the optB88-vdW functional. Partial charge (e) Position Si-H

Phenol

OH

ortho

+2.77

-2.77

-2.34

meta

+2.67

-2.67

-2.23

para

+2.69

-2.69

-2.22


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This has polarised the charge distribution such that the silicene sheet is positively-charged whilst the phenol groups are negatively-charged. For the phenyl-modified silicene18 the charge distribution has been shown to be more uniform with only a small amount of charge (0.02e) being transferred to the phenyl groups. This polarization of charge in the phenol-modified silicene may allow it to be dissolved in polar solvents and hence used in applications where for example the nanomaterial is used in an aqueous environment. The calculated band gaps for each of the ortho-, meta- and para- phenol-modified silicene structures are presented in Table 4. We note that while it is well known that DFT methods (such as those used here) do not accurately represent the experimentally determined band gap, they are valid for determining trends and changes in the size of the band gap. When vdW interactions are considered there are smaller differences in the band gaps for each of the substitution sites. The band structures for the vdW-DFT (optB88) method are shown in Figure 3. Those calculated using the DFT-PBE functional and DFT-D2 Grimme method are shown in Figures S4 and S5, respectively. The band gap was found to be direct (at the Gamma point), irrespective of the substitution position of the OH group, and the size of the band gap was also found to be the same (1.93 eV). This value is 0.06 eV lower than the phenyl-modified silicene we investigated in our previous work.17,18 Interestingly, the DFT-D2 method of Grimme and vdW-exclusive PBE method produced larger differences in the band gap but the overall band dispersions were similar. This means that DFT-D2 and PBE show stronger dependence of the band gap on the OH substitution position than vdW-DFT optB88. A direct gap was also calculated previously for phenyl-modified silicene,8,17,18 however, this is in contrast to other organo-modified silicenes, such as alkoxylated and aminated silicene,8 which result in an indirect gap.


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Figure 3. Band structure of the relaxed monolayer organosilicon nanosheet for the (a) ortho- (b) meta- and (c) para-substituted OH groups, calculated with vdW-DFT using the optB88 functional.

Figures 4a) and b) show the partial density of states using vdW-DFT (optB88) for the paraand meta-substituted structures, respectively. It is clear that the DOS for these structures are very similar to each other. In both cases the Si px,y states are seen to contribute strongly to the top of the valence band and the Si s and pz states are contributing most to the bottom of the conduction band. Whilst no difference has been observed in contributing states for the valence band (in comparison to phenyl-modified silicene), we have seen an increase in the contribution of the C 2px,y states to the conductance band. The oxygen atoms contribute primarily to states at approximately 1 eV below the top of the valence band and overlap with those of the C px, py, and pz states as they are bonded to each other in the phenol groups. There are no major contributions


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from the oxygen atoms to the top of the valence band or bottom of the conduction band, respectively, explaining why there is little change in the size of the band gap compared to the phenyl-modified silicene.

Figure 4. Partial density of states of the (a) para- and (b) meta-substituted phenol-modified silicene, calculated with vdW-DFT (optB88). The region surrounding the band gap is magnified (inset).


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Table 4. Calculated band gap (eV) for each of the phenol-modified silicene structures, using the different density-functional-based methods. Band gap (eV) Position

DFT (PBE)

DFT-D2 (Grimme)

vdW-DFT (optB88)

ortho

1.69

1.73

1.93

meta

1.95

1.95

1.93

para

1.88

1.90

1.92

Hence, we have shown that the polarity of phenyl-modified silicene can be altered by introducing hydroxyl groups, while retaining very similar electronic properties. The calculated vibrational density of states for the para-substituted structure is shown in Figure 5. Such a plot can be related to an IR spectrum obtained experimentally and could be used to help identify the structure. The VDOS here show a strong similarity with the VDOS of the phenyl-modified silicene15 with the peaks associated with the ν(C-H) and ν(Si-H) stretches seen at ~3100 cm-1 and ~2100 cm-1, respectively. In addition, the peaks related to the stretching modes for C=C (~1500-2000 cm-1) and Si-Ph (~1000-1400 cm-1) can also be seen. There is also a series of small peaks due to O between ~1050-1300 cm-1 which may be attributed to a C-O stretching mode. We note, however, that it is difficult to identify peaks associated with any O-H stretch but this may be due to the low number of such groups in the structure and their expected location at high frequencies. Overall, the VDOS of the phenol-modified silicene shows fewer well defined peaks than the phenyl-modified silicene, with broader features, suggesting that the 2D Si network structure is somewhat more flexible. Indeed we do see some flexing of the nanosheet as the phenol groups tilt on the surface in order to form hydrogen bonds.


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Figure 5. (a) Total vibrational DOS (VDOS) for the para-substituted phenyl-modified silicene. (b), (c), (d) and (e) partial VDOS for Si, C, O and H, respectively. The peaks associated with n(C–H) and n(Si–H) are indicated by solid blue and black arrows, respectively. The insets show the low frequency region of the partial VDOS on an enlarged scale.

Unlike the phenyl-modified structure, there are no clear peaks corresponding to the rotation and bending modes (as seen in partial VDOS for C). This suggest a different dynamical behavior


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compared to the phenyl-modified structure. By examining the phenol groups during the MD simulation, we see that there is less rotation of the groups on the sheet due to the tilting of the groups on the sheet so they can align closer to each other due to the hydrogen-bond attraction. Overall, the calculations show that termination of silicene with phenol groups opens the band gap, removing the Dirac cone. While this may lead to properties that are not suitable for some applications of silicene (where a gapless material is required), it could make silicene suitable as a component in field effect transistors (FETs). The added advantage of organo-functionalized silicene is that it is highly resistant to oxidation16,35,36 which is important for operation of devices under atmospheric conditions.

CONCLUSIONS We have examined the properties of phenol-modified silicene using DFT and DFTB calculations and ab initio molecular dynamics simulations. We tested substituting the hydroxyl group at the ortho-, meta- and para- positions on the phenyl ring. We showed that it is necessary to include van der Waals forces to represent the interaction between the functional groups on the silicene sheet. The most stable structure was para-substituted phenol silicene, followed by the meta- and then ortho-substituted structures, however, the para- and meta-substituted structures are of almost equal stability and we suggest that they could occur with almost equal probability. We showed that the phenol groups on the nanosheet will rotate around so that the OH groups on adjacent rings are located close enough together so that they form hydrogen bonds with each other. The band gap for the para-substituted structure was only slightly larger than the phenylmodified system, indicating that both nanosheets would have similar electronic properties. We suggest, however, that the presence of the OH groups in the nanosheet studied here may provide


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unique binding sites for other molecules to adsorb, such as for gas sensing applications. Furthermore, the polar properties of the OH groups may allow the nanosheets to dissolve better in hydrophilic solvents, allowing for different applications of this unique nanomaterial.

ASSOCIATED CONTENT Supporting Information. Figures S1-S6. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Authors * [email protected]; phone

61-3-9925-9697; fax 61-3-9925-3747;

http://www.rmit.edu.au/staff/michelle-spencer * [email protected]; phone

81-29-861-3602; fax 81-29-861-3171;

http://staff.aist.go.jp/t-morishita/ Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding Sources The authors declare no competing financial interest.

ACKNOWLEDGMENT


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TM and MJSS would like to thank Hideyuki Nakano for useful discussions. The computations were undertaken with the assistance of resources from the National Computational Infrastructure (NCI), which is supported by the Australian Government, the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia, the Multi-modal Australian ScienceS Imaging and Visualisation Environment (MASSIVE), and the Victorian Partnership for Advanced Computing Limited (VPAC Ltd) through the V3 Alliance, Australia: and facilities at the Research Centre for Computational Science, National Institute of National Sciences, and the Research Institute for Information Technology, Kyushu University, Japan. This work was also supported in part by a Grant-in-Aid for Scientiﬁc Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

ABBREVIATIONS MD, molecular dynamics; DOS, density of states;

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Table of Contents Graphic and Synopsis Here


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Phenol-Modified Silicene: Preferred Substitution Site and Electronic

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