Adsorption of lanthanide double-decker phthalocyanines on single-walled carbon nanotubes: structural changes and electronic properties as studied by density functional theory

Context Molecular modeling of carbon nanotubes and lanthanide double-decker phthalocyanines hybrids is challenging due to the presence of 4f-electrons. In this paper, we analyzed the trends in structural changes and electronic properties when a lanthanide (La, Gd, and Lu) bisphthalocyanine molecule is adsorbed on the surface of two single-walled carbon nanotubes (SWCNTs) models: armchair and zigzag. The density functional theory (DFT) computations showed that the height of bisphthalocyanines complexes (LnPc2) when adsorbed on a nanotube (LnPc2+SWCNT) is the structural feature which is most affected by the nanotube model. The formation energy of the LnPc2+SWCNT hybrid depends on the metal atom and the nanotube chirality. LaPc2 and LuPc2 bind stronger to the zigzag nanotube, while for GdPc2, bonding to the armchair nanotube is the stronger one. The HOMO-LUMO gap energy (Egap) shows a correlation between the nature of lanthanide and the nanotube chirality. In the case of adsorption on armchair nanotube, Egap tends to match the gap of isolated LnPc2, whereas for adsorption on the zigzag nanotube, it is closer to the value for the isolated nanotube model. The spin density is localized on the phthalocyanines ligands (plus on Gd in the case of GdPc2), when the bisphthalocyanine is adsorbed on the surface of the armchair nanotube. For bonding to zigzag nanotube (ZNT), it extends over both components, except for LaPc2+ZNT, where spin density is found on the nanotube only. Method All DFT calculations were carried out using the DMol3 module of Material Studio 8.0 software package from Accelrys Inc. The computational technique chosen was the general gradient approximation functional PBE in combination with a long-range dispersion correction developed by Grimme (PBE-D2), the double numerical basis set DN, and the DFT semi-core pseudopotentials. Supplementary Information The online version contains supplementary material available at 10.1007/s00894-023-05557-w.


Introduction
The lanthanide double-decker phthalocyanine complexes (also known as bisphthalocyanines) are composed of (usually) a trivalent lanthanide atom (Ln 3+ ), which is coordinated with a dianionic macrocycle Pc 2and a monoanionic radical ligand Pc •-(that is, [Ln 3+ (Pc 2-)(Pc •-)]; hereafter LnPc 2 ) [1][2][3][4][5]. This class of complexes has attracted great interest due to their remarkable electronic and optical properties, and especially because of their single-molecule magnet (SMM) behavior. In fact, they show a large magnetic anisotropy, slow relaxation of the magnetic moment, and quantum tunneling of magnetization, which makes them promising candidates for applications in spintronics and quantum computing. These molecular quantum magnets offer the spin degree of freedom that can be used to control the charge transport in conducting systems [6,7].
In view of their inclusion in spintronic devices, hybrids of LnPc 2 with carbon nanomaterials such as graphene and CNTs received special attention, because there the weak spin-orbit coupling is expected to result in long spin coherence lifetimes and lengths [7]. In the case of CNTs, the noncovalent interaction with lanthanide double-decker phthalocyanines (LnPc 2 +CNTs) thorough π-π stacking is a way to improve the magnetic measurements and bistability of SMMs because the main magnetic properties of rare-earth metal center are preserved [18]. Despite this, LnPc 2 +CNTs hybrids either obtained by covalent or non-covalent functionalization of the carbon nanotubes surface have been the least explored both experimentally and computationally, contrary to transition metal phthalocyanines (monophthalocyanines, also called single-decker phthalocyanine, MPc; M(II) = Mn, Fe, Co, Ni, Cu, Zn) [4,6,[18][19][20][21].
In our earlier work [22] dealing with rare-earth doubledecker phthalocyanines, we studied the non-covalent interaction of unsubstituted yttrium bisphthalocyanines (YPc 2 ) with single-walled carbon nanotubes (SWCNTs) by density functional theory (DFT; namely, by using the Perdew-Burke-Ernzerhof functional, PBE, and Grimme's dispersion correction), analyzed structural changes in the two Pc ligands of YPc 2 resulting from π-π interaction with the nanotube sidewalls. Other aspects we addressed were the changes in electronic characteristics upon the YPc 2 adsorption, the effect of nanotube chirality and of the size of double numerical basis sets available in DMol 3 module (DN, DND, and DNP). Compared to MPc and YPc 2 hybrids with nanotubes [22][23][24], graphene [25,26], and fullerenes [27,28], the same computational task for systems including lanthanide derivatives is computationally much more demanding. As in the case of YPc 2 , a second large-size C 32 H 16 N 8 ligand is present, which, when combined with the computational challenge of the 4f electrons from Ce to Lu, and thus with the appearance of a series of highly degenerate states, dramatically complicates the self-consistence field (SCF) convergence.
In order to proceed with DFT studies of non-covalent hybrids of LnPc 2 complexes with carbon nanomaterials, it is crucial to obtain the optimized bisphthalocyanine structures, which represent as closely as possible to the ones obtained experimentally by X-ray diffraction (XDR). We focused on this aspect in our previous report [29]. As opposed to what could be logically expected, the larger DND and DNP basis sets (having polarization functions) were found not to be the best choice for the above purpose, due to (often) unresolvable SCF problems and distorted LnPc 2 geometries (for example, an eclipsed conformation instead of the typical staggered one). Only the use of a smaller DN basis set helped to complete computations for all lanthanides from La to Lu, as well as to obtain reasonable LnPc 2 geometries. Another recent study [30] on other lanthanide-containing systems (endohedral Ln@C 60 fullerenes) showed that the use of DN and DND bases yields essentially the same geometrical and electronic features, as with the ytrium bisphthalocyanine system mentioned above. Therefore, to achieve the main goal of the present work, consisting in the analysis of structural changes and electronic properties of LnPc 2 phthalocyanines (represented by LaPc 2 , GdPc 2 and LuPc 2 ) in LnPc 2 +SWCNTs non-covalent hybrids, we employed the DN basis set along with the PBE-D2 functional.

Computational methods
The geometry optimizations and calculations of energies and electronic characteristics of LnPc 2 +SWCNTs hybrids were performed by using the numerical-based DFT module DMol 3 available as part of the Materials Studio 8.0 software from Accelrys, Inc. [31][32][33][34]. The general gradient approximation (GGA) functional by Perdew-Burke-Ernzerhof (PBE) [35] in combination with a long-range dispersion correction by Grimme [36] (PBE-D2) was the computational technique of choice, because dispersion interactions need to be taken into account, when noncovalently bonded molecular systems are analyzed such as the complexes of tetraazamacrocyclic (including porphyrins and Pcs) and many other compounds with fullerene [27,37], graphene [25,26] and carbon nanotube models [22-24, 38, 39]. Moreover, there are already theoretical studies involving specifically MPc 2 complexes that employed this functional [9,[40][41][42][43]. As in a recent study by our group on the optimization of geometry of lanthanide bisphthalocyanines [29], in all calculations, we employed the DFT semi-core pseudopotentials (DSPP; specially designed to use within DMol 3 module), which implement relativistic effects and spin-orbit coupling, and the double numerical basis set DN, without polarization functions included (equivalent of 6-31G). A global orbital cutoff was set to 4.3 Å (defined by the presence of Ln atoms), and the convergence criteria were as follows: energy gradient, 10 -5 Ha; maximum force, 0.02 Ha/Å; maximum displacement 0.05 Å; SCF tolerance, 10 -4 ; and maximum step size 0.1 Å. As an auxiliary tool to facilitate SCF convergence [29], thermal smearing was used with a target value of 10 -4 Ha (equivalent temperature of 31.6 K).
The formation energies ΔE LnPc2+SWCNT (hereafter ΔE for simplicity) for the noncovalent hybrids of LnPc 2 with SWCNTs models were calculated according to the general equation: where E i is the corresponding absolute energy.

Structural characteristics
To analyze the structural characteristics and electronic properties of LnPc 2 +SWCNTs hybrids, the geometry of each isolated component was optimized first. Two single-walled carbon nanotube models of different chirality were employed: armchair and zigzag, referred to as ANT and ZNT, which are composed of 180 carbon atoms with 8.23 and 7.67 Å diameter and 17.05 and 18.60 Å length, respectively, and whose ends are capped with fullerene hemispheres (Fig. 1).
As representative LnPc 2 complexes, we considered the species with a totally empty (LaPc 2 , electronic configuration [Xe]4f 0 ), a half-filled (GdPc 2 , [Xe]4f 7 ) and a totally filled (LuPc 2 , [Xe]4f 14 ) 4f shell. It was impossible to complete the geometry optimization of LnPc 2 +SWCNTs hybrids without the use of thermal smearing, but the value of 10 -4 Ha applied here is very low (equivalent temperature of 31.6 K). At the same time, the structure optimization for LaPc 2 , GdPc 2 and LuPc 2 was afforded also with Fermi occupancy [29]. Structural comparison of isolated phthalocyanines and those adsorbed on the surface of nanotubes [22][23][24] and other carbon nanomaterials such as the endohedral fullerene Sc 3 N@C 80 [37] and graphene with defects [25,26] revealed an important typical feature of these macrocycles, namely, a strong bending distortion of Pc ligands upon interaction, increasing in such a way the area of Pc contact with the latter: in particular, this was observed for free-base H 2 Pc, its 3d transition metal(II) complexes, as well as yttrium double-decker phthalocyanine interacting with SWCNTs models. This bending due to non-parallel π-π interactions between the two extended π systems occurs to a variable degree, depending on the central atom, the diameter and chirality of the carbon nanotubes [22-24, 44, 45]. The structural parameters we used to characterize such a distortion for each LnPc 2 in the isolated and the adsorbed state in LnPc 2 +SWCNTs hybrids (Table 1) are the rotation angle between the two Pc ligands (skew angle; φ), the molecular size (width), height, the N-Ln distance, and the N-Y-N angles. In the case of isolated LnPc 2 species, each parameter was compared with the one found in experimentally derived structure XRD from [46,47] (details of such comparisons were described in Ref. [29]). Also, the formation energies, HOMO, LUMO and HOMO-LUMO gap energies (E gap ), the charge and spin of central metal atom (Table 2), as well as the spin density distribution, were analyzed.
As most unsubstituted double-decker phthalocyanines, the ones studied in this work are characterized by a staggered structure (Fig. 1), where the mutual rotation angles between Pc ligands approaches 45° [3,29]. The corresponding values for the optimized LaPc 2 and GdPc 2 complexes do not show tangible differences compared to the experimental XRD structures (0.38° and 0.09°, respectively), whereas for LuPc 2 this angle differs by 4.9°. This discrepancy can be attributed to the fact that the experimental value refers to Optimized geometries for lanthanide double-decker phthalocyanines LnPc 2 (Ln= La, Gd and Lu) and carbon nanotubes models with armchair (ANT) and zigzag (ZNT) chirality. Atom colors: gray, carbon; white, hydrogen; deep blue, nitrogen; light blue, lanthanum; turquoise blue, gadolinium; green, lutetium the crystalline phase while the theoretical approach considers an isolated molecule, as well as the presence of solvent in the crystal lattice (the reported LuPc 2 structure included [NBu 4 ] + cation, creating very particular chemical environment [47]). In the phthalocyanines adsorbed on the surface of SWCNTs models, the skew angles are not affected: their values vary between 44.8° and 44.9° only, depending on LnPc 2 complex and nanotube chirality.
The size (or width) of LnPc 2 molecules, which is defined as the maximum distance between the two hydrogen atoms at opposite o-phenylene moieties of Pc rings [11,48], is overestimated in all cases (Table 1), fluctuating around 15.0 Å. Hence, the length of the nanotube models is barely sufficient to accommodate one LnPc 2 molecule. As seen in Table 1, the distance between the hydrogen atoms is not the same for all LnPc 2 complexes. Upon adsorption on the SWCNTs models, the o-phenylene moieties are attracted to the nanotube sidewall, leading to a more domed geometry of Pc ligand contacting SWCNTs. The bending distortion is more noticeable when bisphthalocyanines are adsorbed on ZNT, since its diameter is smaller than that of ANT.
It is known that the two Pc ligands of neat LnPc 2 complexes are not planar, exhibiting a different degree of bending in the isoindole units ( Fig. 1 and Ref. [29]), and this Table 1 Size (in Å), height (in Å), Ln-N bond length (Å), and N-Ln-N angle (in degrees) for isolated LnPc 2 molecules and for LnPc 2 bound noncovalently to a single-walled carbon nanotube (LnPc 2 +SWCNTs with SWCNTs = ANT and ZNT), as well as the shortest distances: Ln … C SWCNT , γ-N … C SWCNT and C LnPc2 … C SWCNT (in Å) between LnPc 2 and SWCNT, calculated using the PBE GGA functional with Grimme's dispersion correction in conjunction with DN basis set. The structural parameters for the crystal structure of LnPc 2 obtained from X-ray diffraction [46,47] are listed for comparison  distortion is attributed to the repulsive interaction between the two macrocycles, especially between the o-phenylene rings. A quantitative evaluation of this distortion can be made by analyzing the height of each LnPc 2 complex, which is measured as the distance between the peripheral hydrogen atoms belonging to the opposing Pc ligands [11,49]. The height of La, Gd, and Lu bisphthalocyanine as well as their size (or width) vary within the same molecule, so that it is usually presented as an interval within which the above H ... H distances are found ( Another set of parameters, which can be employed to evaluate the distortion of LnPc 2 , is the length of coordination bonds between the lanthanide and nitrogen atoms of isoindole units (Ln-N). The calculated Ln-N bond lengths in isolated LnPc 2 molecules are 2.536-2.545 Å for LaPc 2 , 2.507-2.529 Å for GdPc 2 , and 2.384-2.400 Å for LuPc 2 , and hence larger than the XRD experimental values (Table 1 and Fig. 2). Figure 2 shows how the Ln-N length in each isolated bisphthalocyanine decreases as the Ln atomic number increases, and that this trend is maintained after adsorption on the nanotube sidewall. The N-Ln-N angles in isolated complexes were analyzed  (Table 1 and Fig. 2), and result underestimated for GdPc 2 , and overestimated for LaPc 2 and LuPc 2 , compared to the experimental values. The angles of most of the bisphthalocyanines increase after deposition on the surface of each model nanotube with respect to the isolated and optimised structure and reflect greater variation in the range, indicating asymmetry and distortion, the exception of the lanthanum double-decker phthalocyanine on the surface of armchair nanotube, the value of the angles decreases, see Table 1 and Fig. 2. For LnPc 2 +SWCNTs, the change in N-Ln-N angle is opposite to that of Ln-N bond lengths: the angles increase from La to Lu. The change become more dramatic in the gadolinium hybrids.
The attraction between the SWCNTs models and LnPc 2 complexes can be characterized in terms of the shortest Ln … C SWCNT , γ-N … C SWCNT and C LnPc2 … C SWCNT distances. For LaPc 2 +ANT and GdPc 2 +ANT closest distance is found between a carbon atom of the nanotube and one of the azomethine nitrogen atoms (γ-N) of the Pc ligand (γ-N ... C SWCNT ; 3.107 and 3.180 Å , respectively), meanwhile for LuPc 2 +ANT and all three LnPc 2 +ZNT hybrids, the closest contact is between carbon atoms, C LnPc2 … C SWCNT . The shortest distance between lanthanide and a carbon atom of the nanotube (Ln ... C SWCNT ; Table 1) is one of the structural parameters that is most sensible to the nanotube model and the Ln species. In the LnPc 2 +ANT series, this distance increases as the lanthanide atomic number increases, from 4.551 Å for LaPc 2 +ANT to 4.619 Å for LuPc 2 +ANT, while an opposite behavior is observed for the LnPc 2 +ZNT series, where it decreases from 4.692 Å for LaPc 2 +ZNT to 4.533 Å for LuPc 2 +ZNT.
It is important to mention that the use of electron smearing technique, as a tool to solve the SCF convergence problems [29,[50][51][52], does not affect the geometry features for isolated LnPc 2 complexes, compared to those computed using Fermi occupancy, when the smearing values are as low as (1-5)x10 -4 Ha.

Adsorption strength and electronic properties
From Table 2, one can see that the complex formation energy (or adsorption energy) depends on the nature of metal. The lowest negative ΔE values of −65.6 and −64.6 kcal/mol were obtained for GdPc 2 +ANT and GdPc 2 +ZNT, respectively, indicative of the strongest binding. For both the ANT and the ZNT series, ΔE increases in the order of GdPc 2 < LuPc 2 < LaPc 2 . Concerning the effect of the nanotube chirality, LaPc 2 and LuPc 2 adsorbed on ZNT show more negative energies than the ones adsorbed on ANT: −55.4 and −60.7 kcal/mol vs. −52.4 and −55.1 kcal/mol, respectively. At the same, an opposite trend can be seen for GdPc 2 +SWCNTs hybrids, though the difference is as small as 1 kcal/mol. In this regard, it is interesting to mention that LaPc 2 +SWCNTs behave similarly to their YPc 2 analogues [22], where the central rare-earth metal has no f-orbitals, and the nanotube models were substantially smaller.
We also calculated HOMO, LUMO and HOMO-LUMO gap energies (Table 2), and analyzed the corresponding frontier orbital plots (Fig. 3). The gap energy for isolated LnPc 2 complexes slightly decreases in the order of LuPc 2 (0.138 eV)> LaPc 2 (0.133 eV)> GdPc 2 (0. 130 eV), as in earlier calculations with Fermi occupancy [22]. Among the nanotube models, ANT exhibits a higher band gap than ZNT (0.551 and 0.001 eV, respectively), similarly to the smaller nanotube models with the same chirality used to study their non-covalent interactions with 3d transition metal(II) MPcs [22,23,39] and YPc 2 [24]. For what concerns the gap energy of the LnPc 2 +SWCNTs hybrids, the following observations can be made. Firstly, for LnPc 2 +ANT hybrids E gap changes linearly with the lanthanide atomic number. The gap becomes slightly larger as the atomic number, and consequently the number of 4f-electrons increases: 0.128 eV for LaPc 2 , 0.131 eV for GdPc 2 , and 0.134 eV for, LuPc 2 . For LnPc 2 +ZNT, trend is opposite, but the E gap values are smaller by one order of magnitude: 0.021, 0.014 and 0.012 eV for LaPc 2 , GdPc 2 and LuPc 2 , respectively. Secondly, comparing the computed gap values of each hybrid with that of the isolated component (Table 2), one can conclude that in the case of LnPc 2 +ANT, E gap tends to approach the one of the respective isolated LnPc 2 , whereas in the LnPc 2 +ZNT series, it is closer to the band gap of the nanotube, a feature that was found also for YPc 2 +SWCNTs dyads [24]. The fact that the gap energy is higher for LnPc 2 +ANT than for LnPc 2 +ZNT dyads, also observed in our earlier studies of hybrids with 3d transition metal(II) MPcs [22,23,39] and YPc 2 [24], can be interpreted as an effect of the nanotube chirality. At the same time, our theoretical band gap values should be taken with a certain precaution, since it is known that they are strongly underestimated when using pure GGA functionals (PBE in particular).
As far as the distribution of frontier orbitals is concerned, Fig. 3 and Fig. S1 illustrate that for isolated LaPc 2 , GdPc 2 , and LuPc 2 , the HOMO and LUMO is localized on the carbon atoms of the macrocycle, specifically at the pyrrole unit, as observed earlier for YPc 2 [24] and LnPc 2 [29] by us and by other research groups at different theoretical levels [40,53]. For LnPc 2 +SWCNTs hybrids, its behavior depends on the nanotube chirality and on the central Ln atom (Fig. 3 and Fig. S2). In the hybrids with ANT, HOMO and LUMO are localized on bisphthalocyanine as in isolated LnPc 2 and in YPc 2 +ANT [22]. In LnPc 2 +ZNT, the frontier orbital distribution varies. In LaPc 2 +ZNT and LuPc 2 +ZNT, HOMO is located exclusively on nanotube, and LUMO on both components; in the case of LuPc 2 +ZNT, the contribution from the nanotube is more notable. In GdPc 2 +ZNT, HOMO extends over both components and LUMO is localized only nanotube, similarly to the case of YPc 2 +ZNT [22]. An additional detail, which can be observed in Fig. 3, is that neither HOMO nor LUMO is localized on the central Ln metal.
One more aspect of interest we addressed is the charge of lanthanide atom (Table 2), as estimated from the Mulliken population analysis. The charge of La, Gd, and Lu in isolated bisphthalocyanines is 1.827, 1.452, and 1.400 e, respectively. In the case of hybridss, the changes are rather random. For LaPc 2 +SWCNTs hybrids, there is an increase by 0.031 e for LaPc 2 +ANT and 0.099 e for LaPc 2 +ZNT. For their GdPc 2 +ANT and GdPc 2 +ZNT, the Gd charge decreases by 0.045 and 0.060 e, respectively. For LuPc 2 +SWCNTs hybrids, the Lu charge increases by 0.019 e for LuPc 2 +ANT but decreases insignificantly, by 0.007 e for LuPc 2 +ZNT. Regardless of the magnitude, the general trend the same as for isolated phthalocyanines, where the Ln charge decreases in the order of LaPc 2 > GdPc 2 > LuPc 2 .
The trend of charge transfer within the hybrids was analyzed since carbon nanotubes and phthalocyanine hybrids Fig. 4 Spin density plots for lanthanides double-decker phthalocyanine (LaPc 2 , GdPc 2 and LuPc 2 ;), SWCNTs models, and LnPc 2 +SWCNTs hybrids (isosurfaces at 0.01 a.u;) calculated by using the PBE GGA functional with Grimme's dispersion correction with the DN basis set. Violet and orange lobes correspond to spin-up and spin-down electrons, respectively have been considered as supramolecular self-assembled donor-acceptor conjugated systems. From Table 2, it is clear that the direction of charge transfer is from the phthalocyanine to the carbon nanotube and is influenced by the chirality of the nanotube and the central coordination metal. For phthalocyanines adsorbed on the surface of armchair nanotubes, the charge transfer increases inversely to the lanthanide atomic number, from 0.079 (LuPc 2 +ANT) to 0.090 e (LaPc 2 +ANT), while for zigzag nanotube hybrids, it increases directly from 0.377 (LaPc 2 +ZNT) to 0.502 e (LuPc 2 +ZNT), and the latter hybrids apparently generate a higher charge transfer. Something particular that can be denoted and associated, is the Ln … C SWCNT distance, for each set of hybrids per chirality, which has opposite behavior to that structural parameter ( Table 1), and that is that the smaller the Ln … C SWCNT distance, the higher the charge transfer.
Spin density plots calculated for the isolated LnPc 2 complexes, the SWCNTs models, and the LnPc 2 +SWCNTs hybrids are presented in Fig. 4 (also in Figs. S1 and S2). The distribution of the spin density in isolated LaPc 2 and LuPc 2 matches closely the HOMO and LUMO distribution discussed above (Fig. 3). In these complexes, the unpaired electrons are found mainly on carbon atoms of the pyrrole unit that are bonded with the nitrogen atoms, as well as a minor contribution from γ-N and isoindole N atoms. This feature is also present in GdPc 2 , but the additional main contribution here comes from the metal.
The spin distribution in the hybrids depends not only on the central metal, but also on the nanotube model. The plots for the LnPc 2 +ANT hybrids very similar to those of the isolated LnPc 2 complexes, while those for the three hybrids with ZNT exhibit notable differences. In all of them, one can observe the presence of unpaired electrons on the closed nanotube ends (as in the isolated ZNT model). No tangible contribution from the bisphthalocyanine can be found in LaPc 2 +ZNT, and only a minor one in that of LuPc 2 +ZNT. This is in contrast to GdPc 2 +ZNT, where the spin density distribution of the isolated GdPc 2 and of ZNT is combined, in the latter the contribution of spin up (violet lobule) and spin down (orange lobule) in the complex is reversed when deposited in armchair nanotubes. Although qualitatively no differences are observed in the spin density of the ligands of each phthalocyanine on the nanotubes, quantitatively it can be deduced that for LaPc 2 on both nanotubes, the ligand that is closer to the nanomaterial wall has a lower density (for ANT 0. Meanwhile, LuPc 2 adsorbed on ANT the ligand has a lower density 0.419 vs. 0.533 e) and on ZNT a higher density (-0.113 vs. -0.143 e). Table 2 specifies also the spin of Ln atoms in isolated and adsorbed double-decker phthalocyanines. One can see that the Ln spin remains relatively constant. For LaPc 2 and LuPc 2 complexes, where the lanthanide(III) ion is in a closed-shell configuration, it is always close to zero. On the other hand, for GdPc 2 where the 4f orbital of gadolinium ion is halffilled, a minor spin transfer of 0.004 and 0.007 e from ANT and ZNT, respectively, was found.

Conclusions
The main results can be summarized as follows: -The height of LnPc 2 complexes adsorbed on nanotubes is one of the structural features which is most affected by the SWCNTs diameter; the distance between H atoms of opposite Pc ligands increases stronger more for the nanotube with the smaller-diameter, because the ligands are more strongly bent and take on a domed geometry. -Ln-N bond length and N-Ln-N angle of lanthanides bisphthalocyanines on nanotubes with both armchair and zigzag follow the same trend as in isolated LnPc 2 , the Ln-N bond length decreases with increasing atomic number of the central metal, while the value of N-Ln-N increases. -The formation energy of LnPc 2 +SWCNTs hybrids depends on the type of lanthanide and the nanotube chirality. LaPc 2 and LuPc 2 bond stronger to the nanotube with armchair chirality than to the zigzag tube, while the opposite occurs in the case of GdPc 2 (though the difference is insignificant). -The HOMO-LUMO gap width correlates with the number of electrons of lanthanide and nanotube chirality. For LnPc 2 +ANT hybrids E gap increases linearly in the order LaPc 2 < GdPc 2 < LuPc 2 , whereas LnPc 2 +ZNT hybrids the trend is opposite and E gap decreases in the order LaPc 2 > GdPc 2 > LuPc 2 . Hybrids resulting from the adsorption on the armchair nanotube have a larger gap compared to the case when LnPc 2 binds to zigzag tube. In the former case, E gap tends to match the gap of isolated LnPc 2 , whereas in the latter case it is closer to the value for zigzag tube alone. -The spin density for LnPc 2 adsorbed on the armchair nanotube is localized on the Pc ligands, for LnPc 2 adsorbed on the zigzag nanotube on both interaction components, and for LaPc 2 deposited on the zigzag tube only on nanotube.