atomistic study of promising catalyst and electrode material for memory capacitors: platinum oxides

Computational Materials Science 79 (2013) 804–810

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Computational Materials Science

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Atomistic study of promising catalyst and electrode material for memorycapacitors: Platinum oxides

0927-0256/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.commatsci.2013.07.021

⇑ Corresponding author. Tel.: +46 18 4713743.E-mail addresses: muhammad.ramzan@physics.uu.se, ramzanrao@gmail.com

(M. Ramzan).

T. Kaewmaraya a, M. Ramzan a,⇑, W. Sun d, M. Sagynbaeva a,c, Rajeev Ahuja a,b

a Condensed Matter Theory Group, Department of Physics and Astronomy, Box 516, Uppsala University, S-751 20 Uppsala, Swedenb Department of Materials and Engineering, Royal Institute of Technology (KTH), S-100 44 Stockholm, Swedenc Talas State University, Kyrgyzstand Applied Materials Physics, Royal Institute of Technology (KTH), S-100 44 Stockholm, Sweden

a r t i c l e i n f o a b s t r a c t

Article history:Received 6 March 2013Received in revised form 14 July 2013Accepted 17 July 2013

Keywords:Electronic structureOptical propertiesHybrid functionalPhonon calculations

Platinum oxides have the technological importance as evidenced by numerous studies concentrating ontheir crystal structures to attain the clear atomistic understanding but the controversy exists between theexperimental and theoretical studies. In our present study, we report the electronic and optical propertiesof crystalline PtO and PtO2 on the basis of Heyd–Scuseria–Ernzerhof (HSE06) functional within the frame-work of the density functional theory (DFT). We present the structural parameters, electronic and opticalproperties of several proposed structures of PtO and PtO2. We find that PtS-type structure of PtO andCaCl2-type structure of PtO2 are the most stable structures of these materials on the basis of hybrid func-tional and they appear to be semiconductors with band gap values of 0.87 eV and 1.85 eV, respectively.The mechanical stability of these structures is also confirmed by calculating the phonon band structures.The corresponding structural parameters are found in good agreement with experimental values.Furthermore, we present the bader charge analysis and optical properties of these phases.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

Platinum oxides have been considered as attractive materialshaving a variety of technological applications. For instance, theyare used as an important constituent in Adams’ catalyst [1], asuperficial phase for oxidizing carbon compounds [2]. In electro-chemistry, formation of thin-film oxides in platinum surfaces canalter the reactivity of anodic processes [5]. Furthermore, other po-tential applications of platinum oxides are electrode materials formemory capacitors [3,4]. Although PtO oxides have already playeda crucial role to some technological applications as listed, funda-mental understanding of these oxides down to the atomic scaleshas not been completed. More studies are essentially needed asthey can possibly guide us more technological advantages.

Typically, platinum oxides can be grown on a Si substrate asthin films and they have been found to exist in several crystallinephases or even an amorphous structure depending on the deposi-tion conditions [14,16]. In particular, the crystalline phases studiedby X-ray diffraction (XRD) have been revealed to have a variety ofstoichiometric formulas namely PtO, PtO1.33 and PtO2 (a-PtO2,b-PtO2, and a

0-PtO2) [17–21,23]. Among these proposed stoichiom-

etric phases, electronic and optical properties of PtO and PtO2 have

been studied by several works in the contexts of both experimentand theory but some issues are still left unclear and questionable[17–21,23–29]. PtO has been originally proposed to crystalize ina tetragonal structure (PtS-type space group P42/mmc) and thisreported atomic structure has been used by many theoretical stud-ies [24–28]. However, there are some debates associated with elec-tronic properties. McBride et al. [14] performed scanning tunnelingmicroscope (STM) experiments and they have reported that PtO isa p-type semiconductor while Abe et al. [15] later argued that it is ametallic conductor. From the theoretical point of views, bothmetallic and semiconducting properties have been found, depend-ing on calculating approaches [24–28]. In addition, Nomiyamaet al. [29] have recently carried out DFT calculations based onthe scope of generalized gradient approximation (GGA) to investi-gate the crystalline structures of PtO and PtO2. They havesuggested a new phase of PtO crystalizing in an orthorhombicstructure (GeS-type space group Pnma) which is energetically themost stable structure as compared to the previously found PtS-type structure. In addition, they have also proposed additionalphases of PtO2 crystalizing in the orthorhombic structure similarto the experimentally-observed b-PtO2 phase i.e.; PbCl2-type struc-ture with space group Pnma and ZrO2-type structure with spacegroup Pbcn. They have found that the orthorhombic PbCl2-typestructure has a slightly different in energy compared to theb-PtO2, suggesting possible existence in experiments. Accordingto the scenario mentioned above, the detailed studies of electronic

T. Kaewmaraya et al. / Computational Materials Science 79 (2013) 804–810 805

and optical properties of these newly proposed structures of PtOand PtO2 are theoretically necessary by employing more reliableapproaches e.g. the method beyond the scope of GGA. This couldintriguingly enable us to theoretically assess their proper atomicgeometries, electronic structures and optical properties with thepredictions of their most energetically stable phases.

The approach of hybrid functional has been demonstrated toreliably predict structural and electronic properties in betteragreement with experiments than the conventional GGAfunctional as numerous materials have been tested [11,12,22].Combining the motivations indicated in the former paragraphand the accuracy of the hybrid functional leads us, to perform the-oretical calculations of PtO (PtS and GeS structures) and ortho-rhombic PtO2 (CaCl2, PbCl2 and ZrO2 structures) within theframework of DFT by using the approach of hybrid functional.For comparison, calculations employing the conventional GGAhave been also carried out to highlight the differences of resultsacquired from the two methodologies. The structural parameters,energetics, and bader charge analysis for each phase are listed.After that, we determine the structure having the lowest energyfor both PtO and PtO2. The electronic properties in terms of densityof states (DOS) and dielectric functions of the lowest-energy struc-ture are given. From our results, we have found that hybrid func-tional predicts PtS-type structure of PtO to be the lowest-energystructure. It exhibits a semiconducting behavior with a band gapof 0.87 eV comparing to metallic phase calculated by GGAfunctional. Furthermore, b-PtO2 is predicted to have the lowest-energy structure among the other allotropes crystallizing inorthorhombic structures and it is a semiconductor with a bandgap of 1.85 eV as compared to the band gap of 0.48 eV obtainedby GGA functional.

Fig. 1. The optimized unit cell geometries of PtO (upper panel), and PtO2 (lowerpanel). The Blue (brown) spheres represent Pt (O) atoms. (For interpretation of thereferences to colour in this figure legend, the reader is referred to the web version ofthis article.)

2. Computational details

In the present study, structural optimization and electronicproperties have been calculated using Vienna Ab-initio SimulationPackage (VASP) [6,7]. The GGA of Perdew, Burke and Ernzerhof(PBE) [8] based on the projector augmented wave (PAW) [9] meth-od was used to treat the exchange–correlation (XC) functional. Tenelectrons (5d96s1) of Pt and 6 electrons (2s22p4) of O, were part ofthe valence electrons in pseudopotentials. The energy cutoff forplane wave basis of 600 eV and k-point mesh for brillouin zonesampling of 10 � 10 � 8 were tested to be sufficient to ensurethe energy convergence of structural optimization. To calculatethe density of states (DOS), the denser k-point mesh was set tobe 24� 24� 10 with the smearing width of 0.05 eV. On the basisof the PBE functional, hybrid functional of Heyd–Scuseria–Ernzerhof(HSE) [10] method has the XC functional empirically defined as thefractional mixture containing Fock exchange, PBE exchange, andPBE correlation as following

EHSExc ¼ 1=4EHF;SR

x ðlÞ þ 3=4EPBE;SRx ðlÞ þ EPBE;LR

x ðlÞ þ EPBEc ; ð1Þ

The PBE exchange term is classified into two parts namely shortrange (SR) and long range (LR). The screening parameters l denotesthe range where the short range term becomes negligible, which istypically 0.207 for HSE06. For structural optimization, the energycutoff for plane wave basis of 600 eV and k-point mesh for brillouinzone sampling of 10 � 10 � 8 were used. In addition, the same en-ergy cutoff and denser k-point mesh of 12 � 12 � 10 were used forDOS calculations with the smearing width of 0.05 eV. Both PBE andHSE06 calculations, the conjugate gradient algorithm for electronicrelaxation was utilized for all the structural optimization. The cellvolume, cell shape, and atomic positions were simultaneously re-laxed until attaining the required accuracy i.e. the Hellman–Feymanforces acting on each atom became less than 0.005 eV/Å.

Based on the electronic ground states determined by DFT, it ispossible to determine the frequency-dependent dielectric proper-ties within the framework of the projector-augmented wavemethod as also implemented in VASP. The imaginary dielectricfunction in the long wavelength limit (q ? 0) is determined fromsumming over the empty states as the following expression

eð2Þab ðxÞ ¼4p2e2

Xlimq!0

1q2

Xc;v;k

2wkdð�c;k � �c;k �xÞ � huckþeaqjuvki

� huckþebqjuvki� ð2Þ

where X is the primitive cell volume, wk is the k-point weights, uck

is the cell periodic part of orbitals at the k-point k, ea is the unitvectors in cartesian coordinates. In addition, v and c represent thevalence band and conduction band states. The imaginary part isused to obtain the real part of dielectric function by using theKramers–Kronig transformation as following

eð1Þab ðxÞ ¼ 1þ 2p

PZ 1

0

eð2Þab ðx0Þðx0Þx02 �x2 dx0 ð3Þ

where P is the principal value. The detailed derivations can be foundelsewhere [13].

3. Results and discussion

3.1. PtO

As mentioned earlier that PtO compounds exist in severalphases depending on experimental conditions, here we initializethe study by determining the ground state structure optimizedby PBE and HSE06 functionals and then discussing about the struc-tural properties. The optimized atomic geometries of PtO crystaliz-ing in PtS-type and GeS-type structures calculated by PBE methodare shown in Fig. 1. The corresponding structural parametersobtained are also listed in Table 1. It can be seen that the unit cell

Fig. 2. The formation energies of PtO (GeS-type and PtS-type) and PtO2 (CaCl2,PbCl2, and ZrO2) calculated from PBE and HSE06 functionals.

806 T. Kaewmaraya et al. / Computational Materials Science 79 (2013) 804–810

of PtS-type structure is composed of two formula units (f.u.) andeach Pt atom is tetrahedrally surrounded by four oxygen atomsas shown in Fig. 1a. The equilibrium lattice parameters of PtS-typePtO are calculated to be a = 3.16(3.13) Å, c = 5.37(5.26) Å by PBE(HSE06), while the reported experimental lattice parameters inRef. [14] are a = 3.078 Å, c = 5.34 Å, respectively. The averagePt–O bond distance and the shortest Pt–Pt distances by PBE(HSE06) are 2.07(2.05) Å and 3.16(3.13) Å, to be compared withthe experimental values of Pt–O and Pt–Pt distances of 2.04 Åand 3.08 Å, respectively. It can be obviously noticed that HSE06functional predicts the lattice constants and bond distances to becloser to the experimental values than calculated by PBE method.

Unlike the PtS-type structure, PtO in the GeS-type structurecontains four formula units and each Pt atom is octahedrallysurrounded by six atoms i.e. four O and two Pt atoms. The calcu-lated lattice parameters by PBE (HSE06) are a = 6.85(6.79) Å,b = 3.40(3.34), c = 4.33(4.26) Å with the average Pt–O bonddistance and the shortest Pt–Pt bond distance of 2.15(2.12) Å and2.58(2.54) Å, respectively. It should be noted that the Pt–Pt bonddistance lies in between that of a crystalline face-centered cubic

Fig. 3. Density of states (DOS) of PtO for both the PtS-typ

(fcc), 2.81 Å and that of a Pt2 molecule, 2.33 Å. This result suggestsa possibility that Pt–Pt bonds could be formed in the GeS-typestructure to create the distorted octrahedral motifs [29]. On theother hand, the Pt–Pt distance in the PtS-type structure is compar-atively about 12% larger than that in the crystalline Pt, suggestingthat no Pt–Pt bonds are formed in the PtS-type structure. In addi-tion, this newly proposed GeS-type structure has been also claimedto be energetically more stable than the PtS-type structure [29],although its experimental existence has not yet been reported.To verify this point, formation energies are also calculated by usingthe following formula.

DHf ¼ EPtOxtot � EPt=atom

tot � xEO2=atomtot ð4Þ

where EPtOxtot is the total energy of PtOx phase, EPt=atom

tot and EO2=atomtot are

total energies of Pt and O atoms. Our calculated formation energiesshown in Fig. 2 support the results presented in Ref. [29]. PBE pre-dicts GeS-type structure to be more stable than PtS-type structurewith the different of formation energy of 110 meV/f.u. On the otherhand, HSE06 predicts that the experimentally-found PtS structure ismore stable than GeS structure with the difference in formation en-ergy of 30 meV/f.u., which is in accord with experimental findings[17] and proves the authentication of HSE06 method to calculatethe correct description of such type of materials.

In order to further probe the bonding characters, bader chargeanalysis was performed and the total electron charges of Pt andO atoms are tabulated in Table II. It can be seen that the calculatedbader charge on Pt (O) atom of PtS-type structure in the unit ofelectron charge (e) is +0.91 (�0.91) e by PBE and 1.02 (�1.02) eby HSE06 while that of GeS-type structure is +0.93 (�0.93) e byPBE and 1.05 (�1.05) e by HSE06, respectively. Our results are ingood agreement with the previous calculations using the same ap-proach and another work using Mulliken population analysis[28,27], further confirming validation of our results. It is obviousthat the charges are less than the nominal oxidation states +2and �2 of Pt and O atoms, respectively, implying that the bondingcharacter is mainly ionic with partial existence of covalent.Furthermore, the ratio between bader charge of Pt and O is 1 to1 which equivalently corresponds to that of +2 and �2 oxidationstates. On the other hand, Pt atoms in GeS-type structureare sixfold instead of fourfold in the PtS-type structure. Theoxidation state of +2 is not allowed according to the octet rule.

e and GeS-type. The fermi level is set at zero energy.

Table IThe calculated lattice parameters of PtO and PtO2 by using PBE and HSE06 functionals.

Compound Structures PBE HSE06

a0 (Å) b0 (Å) c0 (Å) Pt–O (Å) Pt–Pt (Å) a0 (Å) b0 (Å) c0 (Å) Pt–O (Å) Pt–Pt (Å)

PtO GeS 6.85 3.40 4.33 2.15 2.58 6.79 3.34 4.26 2.12 2.54PtS 3.16 3.16 5.37 2.07 3.16 3.13 3.13 5.26 2.05 3.13PtS(Exp.[14]) 3.078 3.078 5.340 2.04 3.08

PtO2 CaCl2 4.61 4.55 3.19 2.04 3.61 4.51 4.55 3.14 2.00 3.57CaCl2(Exp. [23]) 4.48 4.54 3.14PbCl2 9.62 3.16 4.67 2.05 3.59 9.49 3.11 4.62 2.02 3.56ZrO2 5.25 4.56 5.61 2.04 3.11 5.16 4.43 5.53 2.00 3.05

T. Kaewmaraya et al. / Computational Materials Science 79 (2013) 804–810 807

Nomiyama et. al. [29] expect that the oxidation state of Pt to rangebetween +2 and +4. From our bader analysis, Pt and O atoms in theGeS-type structure possess higher charge than those in the PtS-type structure, suggesting that the oxidation state of Pt atomscan be higher than +2.

Electronic properties of PtO are investigated by calculating thedensity of states (DOS) as illustrated in Fig. 3. It can be clearly seenthat PBE functional predicts PtS structure to be metallic but HSE06functional correctly predicts a semiconducting behavior with aband gap of 0.87 eV, significantly bigger than calculated band gapof 0.38 eV by GGA + U (U = 9 eV) [28]. Furthermore, the band gapis consistent with that calculated by the augmented spherical wave(ASW) approach and linear muffin-tin orbital method (LMTO)[24,26]. Fig. 3 also shows the decompositions of partial Pt-5d andO-2p states. The Pt-5d states are dominant close to the fermi levelwhereas the O-2p states are formed at lower energy away from thefermi level. At the bottom of the conduction band, Pt-5d states aremore dominant than O-2p states. The obvious d–p hybridizationappears at the bottom of the conduction band positioned between2 and 4 eV.

For the GeS structure, both PBE and HSE06 predict a semicon-ducting behavior with the band gaps of 0.30 eV and 1.80 eV,respectively as indicated in the right panel of Fig. 3. The Pt-5dstates play an important role at the upper part of the valence band.Unlike PtS structure, the top of the valence band is a mixture of

Fig. 4. Density of states of PtO2 (CaCl2, PbCl2 and ZrO

Pt-5d and O-2p states and the corresponding d–p hybridization isobserved. This hybridization can be considered as the Pt-5d andO-2p bonding states. Similarly, d–p hybridization is also clearlyseen at the bottom of conduction band and it represents Pt-5dand O-2p anti-bonding states. It can also be pointed out that mored–p hybridization is comparatively seen in the GeS structure ascompared to PtS structure. This supports the bader charge analysisin Table II that more charges are transferred between Pt and O inthe case of GeS structure. Furthermore, the band gap of PtS-typestructure is smaller than that of GeS-type structure. This can beexplained by using the crystal field theory. In octahedral crystalfield, the magnitude of splitting of d orbitals into eg and t2g arehigher than tetrahedral field due to more ligands. Since, the topof the valence band and the bottom of the conduction band aremainly formed by d states, the stronger d splitting results in biggerband gap. It should be also noted that DOS of PtO evaluated by PBEand HSE06 have the same feature except the shift in the conduc-tion band upward to separate occupied and unoccupied states.

3.2. PtO2

Another experimentally known crystalline phase of platinumoxides reported for PtO2 is b-PtO2 crystalizing in orthorhombicCaCl2 structure with space group (Pnnm). As previously stated,other two possible phases have been theoretically suggested by

2 structures). The fermi energy is shifted to zero.

Table IIThe bader charge of Pt and O atoms in PtO and PtO2 in the unit of electron charge. Thevalues obtained from HSE06 functional are presented in the parentheses.

Structure Pt charge O charge

PtO (GeS-type) +0.91(+1.02) �0.91(�1.02)PtO (PtS-type) + 0.93(+1.05) �0.93(�1.05)PtO2(CaCl2-type) +1.72(+1.98) �0.86(�0.99)PtO2(PbCl2-type) + 1.69(+1.91) �0.84(�0.95)PtO2(ZrO2-type) + 1.72(+1.98) �0.87(�0.99)

808 T. Kaewmaraya et al. / Computational Materials Science 79 (2013) 804–810

Nomiyama et al. [29] to exist with total energies almost degeneratewith b-PtO2 and they also crystallizes in orthorhombic similar tob-PtO2 with space group Pnma (PbCl2-type structure) and spacegroup Pbcn (ZrO2-type structure). Fig. 1 displays the optimizedatomic geometries of these three PtO2 phases and their corre-sponding equilibrium lattice parameters are listed in Table I. Itcan been seen that each Pt atom is now octahedrally coordinatedby six O atoms to have octahedral motifs with different orienta-tions. Table I indicates that lattice parameters determined byHSE06 are comparatively shorter than those calculated by PBE.However, our results by PBE are in good agreement with the previ-ous work [29,28]. In particular, we obtain the lattice parameters ofCaCl2-type structures by HSE06 obviously to be closer to experi-mental values than PBE. This is possible to conclude that hybrid-DFT predicts lattice parameters of b-PtO2 more correctly than theconventional PBE.

In terms of stability, the formation energies of PtO2 phases areshown in Fig. 2. Comparatively, it can be seen that all the PtO2

structures have lower formation energies than PtO, indicating thatthey are thermodynamically more stable. PBE and HSE06 predictthe same trend that CaCl2-type structure is the most stable one.Even though our PBE result is in good agreement with the previouswork, it should be pointed out that CaCl2-type and PbCl2-typestructures are almost degenerate with the energy difference of10 meV/f.u. ZrO2-type structure has higher energy than the firsttwo with the energy different of approximately 80 meV/f.u. Onthe other hand, HSE06 predicts CaCl2 structure to be notably themost stable with lower formation energy more than 65 meV/f.u.

Fig. 5. Phonon band structures and corresponding first brillouin zones of P

as compared to the PbCl2 and ZrO2 structures. However, PbCl2

and ZrO2 structures are nearly degenerate with the energy differ-ence of only 20 meV/f.u. Electronic properties of PtO2 are studiedby presenting DOS as shown in Fig. 4. Unlike PtO, all the PtO2 allo-trope calculated by PBE exhibit semiconducting behaviors. The cor-responding band gaps of CaCl2-type, PbCl2-type and ZrO2-typestructures are 0.48 eV, 0.76 eV and 0.45 eV, respectively. ThesePBE band gaps are in accord with the previous findings [29]although their experimental values have not yet been reported.DOSs show that Pt-5d and O-2p almost equally contribute to thetop of the valence band and obvious hybridization of p–d statesare observed. On the other hand, Pt-5d states are more dominantat the bottom of the conduction band with noticeable p–d hybrid-ization. It should be noted that Pt-5d and O-2p states of PbCl2-typestructure are comparatively more localized at the conduction band.This is also supported by bader charge analysis presented inTable II that bader charges of Pt and O atoms are comparativelyless than those in CaCl2 and ZrO2 structures. The bader chargesof Pt and O atoms in CaCl2-type and ZrO2-type structures are iden-tical and the same Pt–O bond distances of these two structuresindicated in Table I can be evidenced. Comparatively, the Pt–Obond distances of PtO2 are shorter than PtO, implying strongerPt–O bonds. Furthermore, the ratio of bader charge of Pt and Oatoms is 2:1 for all the allotropes, implying the oxidation state ofPt and O to be +4 and �2, respectively. For the hybrid HSE06, thecalculated DOSs broadly have the same features as calculated byPBE despite of larger band gaps between the occupied and unoccu-pied states. The calculated band gaps of CaCl2-type, PbCl2-type andZrO2-type structures are 1.85 eV, 2.48 eV and 1.96 eV, respectively.It is noted that the band gap of the CaCl2-type structure has beenrecently reported to be 1.81 eV by the HSE06 and 1.46 eV by theself-consistent GW approach [30]. The existence of band gaps ofPtO2 can be explained by the effect of octahedral coordination ofO atoms. Crystal-field theory predicts the dxy,dyz and dxz states tobe degenerate forming the t2g state whereas the remaining dz2

and dx2þy2 states are degenerate forming the Eg state. The Pt atomhas d6 configuration that the t2g states are occupied and they areseparated from the empty Eg states, leading to an insulating

tO in PtS-type structure (left) and PtO2 in CaCl2-type structure (right).

Fig. 6. The dielectric functions of PtO (PtS-type) and PtO2 (CaCl2-type).

T. Kaewmaraya et al. / Computational Materials Science 79 (2013) 804–810 809

behavior [28]. Furthermore, the band gaps of PtO2 are larger thanthe gap of PtO (PtS structure). This can be explained by the magni-tude of splitting between the t2g and Eg states. The magnitude ofsplitting is larger in the case of PtO2 due to higher ligands.

3.3. Phonon calculations

As we have already established that PtO in PtS-type structureand PtO2 in CaCl2-type structure are the most stable ones amongother candidate structures. We have also calculated phonon bandstructures based on the supercell approach to acquire insights intotheir mechanical stabilities. We have considered the supercellscontaining 72 atoms and 156 atoms for PtO in PtS-type structureand PtO2 in CaCl2-type structure, respectively. Atoms in the sup-percells are displaced from their equilibrium positions and forcesacting on all the atoms are directly determined by using VASP.These forces are subsequently collected to calculate phonondispersions by using PHONOPY package [31]. Our findings clearlyindicate that no imaginary frequencies are found in phonon bandstructures illustrated below in Fig. 5, further theoretically confirm-ing their mechanical stabilities.

3.4. Dielectric properties

We have also calculated the dielectric properties of the moststable structures of PtO and PtO2, predicted by hybrid density func-tional (HSE06), with the use of PBE and HSE06 functionals as wehave already described in the computational details. From Fig. 6,we can see that the optical band gaps calculated by either PBE orhybrid density functional are in agreement with the electronicband gaps calculated by density of states (DOS) for PtO and PtO2

materials. All the peaks are also at the same positions as we haveseen in the partial density of states (PDOS) either calculated byPBE or HSE06 method.

4. Conclusion

In summary, we have studied the all candidate structures of po-tential technological materials: PtO and PtO2, with the use of PBEand hybrid functional (HSE06) to find the most stable structures,which were necessary to resolve the controversy between the

experimental and theoretical studies. The structural and electronicproperties of these materials are also investigated and our calcu-lated structural parameters with the use of HSE06 functional arein good agreement with the available experimental data in the lit-erature. Our calculated bader charge analysis are in accordancewith the density of states, which makes us confident about thecorrectness of our calculation method. We predict that PtS-typestructure for PtO and CaCl2 -type structure for PtO2 are the moststable structures on the basis of hybrid density functional method(HSE06). Phonon band structures are also calculated to confirm themechanical stability of these structures. Moreover, we havepresented the optical properties of these materials. We hope thatour work will be helpful to understand the correct description ofsuch type of oxide materials, which are very important forscientific as well as technological communities.

Acknowledgements

We would like to acknowledge Swedish Energy Agency (STEM)and Carl Trygress Foundation (CTS) for financial support. T.K.would like to acknowledge the Royal Thai Government for financialsupport. M. Ramzan is thankful to the Higher Education Commis-sion of Pakistan (HEC) for Ph.D. studentship. M. Sagynbaevaacknowledges Erasmus Mundus MarcoXXI program for financialsupport. SNIC and UPPMAX have provided computing time for thisproject.

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