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Volumn 140, Issue 16, 2014, Pages

The Raman spectrum of CaCO3 polymorphs calcite and aragonite: A combined experimental and computational study

Author keywords

[No Author keywords available]

Indexed keywords

CALCITE; CALCIUM CARBONATE; RAMAN SCATTERING; SINGLE CRYSTALS;

EID: 84899889166     PISSN: 00219606     EISSN: None     Source Type: Journal    
DOI: 10.1063/1.4871900     Document Type: Article
Times cited : (147)

References (64)
  • 2
    • 0041345901 scopus 로고    scopus 로고
    • Calcium carbonate in biomineralisation and biomimetic chemistry
    • 10.1179/095066003225005836
    • F. C. Meldrum, " Calcium carbonate in biomineralisation and biomimetic chemistry," Int. Mater. Rev. 48, 187-224 (2003). 10.1179/095066003225005836
    • (2003) Int. Mater. Rev. , vol.48 , pp. 187-224
    • Meldrum, F.C.1
  • 5
    • 82955190561 scopus 로고    scopus 로고
    • A new structural model for disorder in vaterite from first-principles calculations
    • 10.1039/c1ce05976a
    • R. Demichelis, P. Raiteri, J. D. Gale, and R. Dovesi, " A new structural model for disorder in vaterite from first-principles calculations," Cryst. Eng. Comm. 14, 44-47 (2012). 10.1039/c1ce05976a
    • (2012) Cryst. Eng. Comm. , vol.14 , pp. 44-47
    • Demichelis, R.1    Raiteri, P.2    Gale, J.D.3    Dovesi, R.4
  • 6
    • 84878663898 scopus 로고    scopus 로고
    • The multiple structures of vaterite
    • 10.1021/cg4002972
    • R. Demichelis, P. Raiteri, J. D. Gale, and R. Dovesi, " The multiple structures of vaterite," Cryst. Growth Des. 13, 2247-2251 (2013). 10.1021/cg4002972
    • (2013) Cryst. Growth Des. , vol.13 , pp. 2247-2251
    • Demichelis, R.1    Raiteri, P.2    Gale, J.D.3    Dovesi, R.4
  • 8
    • 0010675067 scopus 로고
    • Vibrational spectra of single ionic crystals
    • L. Couture, " Vibrational spectra of single ionic crystals," Ann. Phys. 2, 5-94 (1947).
    • (1947) Ann. Phys. , vol.2 , pp. 5-94
    • Couture, L.1
  • 10
    • 84872089203 scopus 로고    scopus 로고
    • The vibrational spectrum of CaCO3 aragonite: A combined experimental and quantum-mechanical investigation
    • 10.1063/1.4772960
    • C. Carteret, M. De la Pierre, M. Dossot, F. Pascale, A. Erba, and R. Dovesi, " The vibrational spectrum of CaCO3 aragonite: A combined experimental and quantum-mechanical investigation," J. Chem. Phys. 138, 014201 (2013). 10.1063/1.4772960
    • (2013) J. Chem. Phys. , vol.138 , pp. 014201
    • Carteret, C.1    De La Pierre, M.2    Dossot, M.3    Pascale, F.4    Erba, A.5    Dovesi, R.6
  • 11
    • 36049060591 scopus 로고
    • Depolarization of raman scattering in calcite
    • 10.1103/PhysRev.147.608
    • S. P. S. Porto, J. A. Giordmaine, and T. C. Damen, " Depolarization of raman scattering in calcite," Phys. Rev. 147, 608-611 (1966). 10.1103/PhysRev.147.608
    • (1966) Phys. Rev. , vol.147 , pp. 608-611
    • Porto, S.P.S.1    Giordmaine, J.A.2    Damen, T.C.3
  • 12
    • 32544440773 scopus 로고    scopus 로고
    • Raman spectroscopy - A powerful tool for the quantitative determination of the composition of polymorph mixtures: Application to CaCO3 polymorph mixtures
    • 10.1002/ceat.200500354
    • A. Dandeu, B. Humbert, C. Carteret, H. Muhr, E. Plasari, and J.-M. Bossoutrot, " Raman spectroscopy-A powerful tool for the quantitative determination of the composition of polymorph mixtures: Application to CaCO3 polymorph mixtures," Chem. Eng. Technol. 29, 221-225 (2006). 10.1002/ceat.200500354
    • (2006) Chem. Eng. Technol. , vol.29 , pp. 221-225
    • Dandeu, A.1    Humbert, B.2    Carteret, C.3    Muhr, H.4    Plasari, E.5    Bossoutrot, J.-M.6
  • 13
    • 61749085640 scopus 로고    scopus 로고
    • Polymorphism studied by lattice phonon Raman spectroscopy and statistical mixture analysis method: Application to calcium carbonate polymorphs during batch crystallization
    • 10.1021/cg800368u
    • C. Carteret, A. Dandeu, S. Moussaoui, H. Muhr, B. Humbert, and E. Plasari, " Polymorphism studied by lattice phonon Raman spectroscopy and statistical mixture analysis method: Application to calcium carbonate polymorphs during batch crystallization," Cryst. Growth Des. 9, 807-812 (2009). 10.1021/cg800368u
    • (2009) Cryst. Growth Des. , vol.9 , pp. 807-812
    • Carteret, C.1    Dandeu, A.2    Moussaoui, S.3    Muhr, H.4    Humbert, B.5    Plasari, E.6
  • 14
    • 0037429620 scopus 로고    scopus 로고
    • Quantitative analysis of synthetic calcium carbonate polymorphs using FT-IR spectroscopy
    • 10.1016/S0039-9140(02)00638-0
    • N. V. Vagenas, A. Gatsouli, and C. G. Kontoyannis, " Quantitative analysis of synthetic calcium carbonate polymorphs using FT-IR spectroscopy," Talanta 59, 831-836 (2003). 10.1016/S0039-9140(02)00638-0
    • (2003) Talanta , vol.59 , pp. 831-836
    • Vagenas, N.V.1    Gatsouli, A.2    Kontoyannis, C.G.3
  • 15
    • 0034913365 scopus 로고    scopus 로고
    • Quantitative determination of binary and tertiary calcium carbonate mixtures using powder X-ray diffraction
    • 10.1039/b103004n
    • S. R. Dickinson and K. M. McGrath, " Quantitative determination of binary and tertiary calcium carbonate mixtures using powder X-ray diffraction," Analyst 126, 1118-1121 (2001). 10.1039/b103004n
    • (2001) Analyst , vol.126 , pp. 1118-1121
    • Dickinson, S.R.1    McGrath, K.M.2
  • 16
    • 0033999465 scopus 로고    scopus 로고
    • Calcium carbonate phase analysis using XRD and FT-Raman spectroscopy
    • 10.1039/a908609i
    • C. G. Kontoyannis and N. V. Vagenas, " Calcium carbonate phase analysis using XRD and FT-Raman spectroscopy," Analyst 125, 251-255 (2000). 10.1039/a908609i
    • (2000) Analyst , vol.125 , pp. 251-255
    • Kontoyannis, C.G.1    Vagenas, N.V.2
  • 18
    • 34247574250 scopus 로고    scopus 로고
    • Ab initio vibrational spectra and dielectric properties of carbonates: Magnesite, calcite and dolomite
    • 10.1007/s00214-006-0213-2
    • L. Valenzano, Y. Noël, R. Orlando, C. M. Zicovich-Wilson, M. Ferrero, and R. Dovesi, " Ab initio vibrational spectra and dielectric properties of carbonates: Magnesite, calcite and dolomite," Theor. Chem. Acc. 117, 991-1000 (2007). 10.1007/s00214-006-0213-2
    • (2007) Theor. Chem. Acc. , vol.117 , pp. 991-1000
    • Valenzano, L.1    Noël, Y.2    Orlando, R.3    Zicovich-Wilson, C.M.4    Ferrero, M.5    Dovesi, R.6
  • 19
    • 84883333645 scopus 로고    scopus 로고
    • Examining the accuracy of density functional theory for predicting the thermodynamics of water incorporation into minerals: The hydrates of calcium carbonate
    • 10.1021/jp4048105
    • R. Demichelis, P. Raiteri, J. D. Gale, and R. Dovesi, " Examining the accuracy of density functional theory for predicting the thermodynamics of water incorporation into minerals: The hydrates of calcium carbonate," J. Phys. Chem. C 117, 17814-17823 (2013). 10.1021/jp4048105
    • (2013) J. Phys. Chem. C , vol.117 , pp. 17814-17823
    • Demichelis, R.1    Raiteri, P.2    Gale, J.D.3    Dovesi, R.4
  • 21
    • 84903362578 scopus 로고    scopus 로고
    • Ab initio analytical Raman intensities for periodic systems through a coupled perturbed Hartree-Fock/Kohn-Sham method in an atomic orbital basis. I. Theory
    • 10.1063/1.4824442
    • L. Maschio, B. Kirtman, M. Rérat, R. Orlando, and R. Dovesi, " Ab initio analytical Raman intensities for periodic systems through a coupled perturbed Hartree-Fock/Kohn-Sham method in an atomic orbital basis. I. Theory," J. Chem. Phys. 139, 164101 (2013). 10.1063/1.4824442
    • (2013) J. Chem. Phys. , vol.139 , pp. 164101
    • Maschio, L.1    Kirtman, B.2    Rérat, M.3    Orlando, R.4    Dovesi, R.5
  • 22
    • 84903362578 scopus 로고    scopus 로고
    • Ab initio analytical Raman intensities for periodic systems through a coupled perturbed Hartree-Fock/Kohn-Sham method in an atomic orbital basis. II. Validation and comparison with experiments
    • 10.1063/1.4824443
    • L. Maschio, B. Kirtman, M. Rérat, R. Orlando, and R. Dovesi, " Ab initio analytical Raman intensities for periodic systems through a coupled perturbed Hartree-Fock/Kohn-Sham method in an atomic orbital basis. II. Validation and comparison with experiments," J. Chem. Phys. 139, 164102 (2013). 10.1063/1.4824443
    • (2013) J. Chem. Phys. , vol.139 , pp. 164102
    • Maschio, L.1    Kirtman, B.2    Rérat, M.3    Orlando, R.4    Dovesi, R.5
  • 23
    • 84899794668 scopus 로고    scopus 로고
    • See supplementary material at E-JCPSA6-140-073416 for additional data.
    • See supplementary material at http://dx.doi.org/10.1063/1.4871900 E-JCPSA6-140-073416 for additional data.
  • 25
    • 33846482863 scopus 로고
    • Raman effect in zinc oxide
    • 10.1103/PhysRev.142.570
    • T. C. Damen, S. P. S. Porto, and B. Tell, " Raman effect in zinc oxide," Phys. Rev. 142, 570-574 (1966). 10.1103/PhysRev.142.570
    • (1966) Phys. Rev. , vol.142 , pp. 570-574
    • Damen, T.C.1    Porto, S.P.S.2    Tell, B.3
  • 26
    • 0000189651 scopus 로고
    • Density-functional thermochemistry 3. The role of exact echange
    • 10.1063/1.464913
    • A. D. Becke, " Density-functional thermochemistry 3. The role of exact echange," J. Chem. Phys. 98, 5648-5652 (1993). 10.1063/1.464913
    • (1993) J. Chem. Phys. , vol.98 , pp. 5648-5652
    • Becke, A.D.1
  • 30
    • 8344242162 scopus 로고    scopus 로고
    • The calculation of the vibration frequencies of α-quartz: The effect of Hamiltonian and basis set
    • 10.1002/jcc.20120
    • C. M. Zicovich-Wilson, F. Pascale, C. Roetti, V. R. Saunders, R. Orlando, and R. Dovesi, " The calculation of the vibration frequencies of α-quartz: The effect of Hamiltonian and basis set," J. Comput. Chem. 25, 1873-1881 (2004). 10.1002/jcc.20120
    • (2004) J. Comput. Chem. , vol.25 , pp. 1873-1881
    • Zicovich-Wilson, C.M.1    Pascale, F.2    Roetti, C.3    Saunders, V.R.4    Orlando, R.5    Dovesi, R.6
  • 34
    • 65249153485 scopus 로고    scopus 로고
    • Ab initio quantum-mechanical simulation of the Raman spectrum of grossular
    • 10.1002/jrs.2144
    • R. Dovesi, L. Valenzano, F. Pascale, C. M. Zicovich-Wilson, and R. Orlando, " Ab initio quantum-mechanical simulation of the Raman spectrum of grossular," J. Raman Spectrosc. 40, 416-418 (2009). 10.1002/jrs.2144
    • (2009) J. Raman Spectrosc. , vol.40 , pp. 416-418
    • Dovesi, R.1    Valenzano, L.2    Pascale, F.3    Zicovich-Wilson, C.M.4    Orlando, R.5
  • 35
    • 81855190689 scopus 로고    scopus 로고
    • The IR vibrational properties of six members of the garnet family: A quantum mechanical ab initio study
    • 10.2138/am.2011.3804
    • R. Dovesi, M. De La Pierre, A. M. Ferrari, F. Pascale, L. Maschio, and C. M. Zicovich-Wilson, " The IR vibrational properties of six members of the garnet family: A quantum mechanical ab initio study," Am. Mineral. 96, 1787-1798 (2011). 10.2138/am.2011.3804
    • (2011) Am. Mineral. , vol.96 , pp. 1787-1798
    • Dovesi, R.1    De La Pierre, M.2    Ferrari, A.M.3    Pascale, F.4    Maschio, L.5    Zicovich-Wilson, C.M.6
  • 37
    • 84858441427 scopus 로고    scopus 로고
    • Electronic structure, dielectric properties and infrared vibrational spectrum of fayalite: An ab initio simulation with an all-electron Gaussian basis set and the B3LYP functional
    • 10.1002/qua.23195
    • Y. Noël, M. De La Pierre, L. Maschio, M. Rérat, C. M. Zicovich-Wilson, and R. Dovesi, " Electronic structure, dielectric properties and infrared vibrational spectrum of fayalite: An ab initio simulation with an all-electron Gaussian basis set and the B3LYP functional," Int. J. Quantum Chem. 112, 2098-2108 (2012). 10.1002/qua.23195
    • (2012) Int. J. Quantum Chem. , vol.112 , pp. 2098-2108
    • Noël, Y.1    De La Pierre, M.2    Maschio, L.3    Rérat, M.4    Zicovich-Wilson, C.M.5    Dovesi, R.6
  • 38
    • 84878108957 scopus 로고    scopus 로고
    • Use of ab initio methods for the interpretation of the experimental IR reflectance spectra of crystalline compounds
    • 10.1002/jcc.23283
    • M. De La Pierre, C. Carteret, R. Orlando, and R. Dovesi, " Use of ab initio methods for the interpretation of the experimental IR reflectance spectra of crystalline compounds," J. Comput. Chem. 34, 1476-85 (2013). 10.1002/jcc.23283
    • (2013) J. Comput. Chem. , vol.34 , pp. 1476-1485
    • De La Pierre, M.1    Carteret, C.2    Orlando, R.3    Dovesi, R.4
  • 39
    • 84899822932 scopus 로고    scopus 로고
    • See, for input and output files.
    • See http://www.crystal.unito.it/supplement/raman-caco3/inpout.tar.gz, for input and output files.
  • 40
    • 0035281512 scopus 로고    scopus 로고
    • Analytical hartree-fock gradients for periodic systems
    • K. Doll, V. R. Saunders, and N. M. Harrison, " Analytical hartree-fock gradients for periodic systems," Int. J. Quantum Chem. 82, 1-13 (2001). 10.1002/1097-461X(2001)82:1<1::AID-QUA1017>3.0.CO;2-W
    • (2001) Int. J. Quantum Chem. , vol.82 , pp. 1-13
    • Doll, K.1    Saunders, V.R.2    Harrison, N.M.3
  • 41
    • 0035370697 scopus 로고    scopus 로고
    • Implementation of analytical hartree-fock gradients for periodic systems
    • 10.1016/S0010-4655(01)00172-2
    • K. Doll, " Implementation of analytical hartree-fock gradients for periodic systems," Comput. Phys. Commun. 137, 74-88 (2001). 10.1016/S0010-4655(01)00172-2
    • (2001) Comput. Phys. Commun. , vol.137 , pp. 74-88
    • Doll, K.1
  • 42
    • 0001027957 scopus 로고    scopus 로고
    • Hartree-Fock geometry optimisation of periodic systems with the CRYSTAL code
    • 10.1016/S0009-2614(01)01081-8
    • B. Civalleri, Ph. D'Arco, R. Orlando, V. R. Saunders, and R. Dovesi, " Hartree-Fock geometry optimisation of periodic systems with the CRYSTAL code," Chem. Phys. Lett. 348, 131-138 (2001). 10.1016/S0009-2614(01)01081-8
    • (2001) Chem. Phys. Lett. , vol.348 , pp. 131-138
    • Civalleri, B.1    D'Arco, Ph.2    Orlando, R.3    Saunders, V.R.4    Dovesi, R.5
  • 43
    • 77958398767 scopus 로고
    • The convergence of a class of double-rank minimization algorithms 1. General considerations
    • 10.1093/imamat/6.1.76
    • C. G. Broyden, " The convergence of a class of double-rank minimization algorithms 1. General considerations," IMA J. Appl. Math. 6, 76-90 (1970). 10.1093/imamat/6.1.76
    • (1970) IMA J. Appl. Math. , vol.6 , pp. 76-90
    • Broyden, C.G.1
  • 44
    • 0014825610 scopus 로고
    • A new approach to variable metric algorithms
    • 10.1093/comjnl/13.3.317
    • R. Fletcher, " A new approach to variable metric algorithms," Comput. J. 13, 317-322 (1970). 10.1093/comjnl/13.3.317
    • (1970) Comput. J. , vol.13 , pp. 317-322
    • Fletcher, R.1
  • 45
    • 84966251980 scopus 로고
    • A family of variable-metric methods derived by variational means
    • 10.1090/S0025-5718-1970-0258249-6
    • D. Goldfarb, " A family of variable-metric methods derived by variational means," Math. Comput. 24, 23-26 (1970). 10.1090/S0025-5718- 1970-0258249-6
    • (1970) Math. Comput. , vol.24 , pp. 23-26
    • Goldfarb, D.1
  • 46
    • 84968497764 scopus 로고
    • Conditioning of quasi-Newton methods for function minimization
    • 10.1090/S0025-5718-1970-0274029-X
    • D. F. Shanno, " Conditioning of quasi-Newton methods for function minimization," Math. Comput. 24, 647-656 (1970). 10.1090/S0025-5718-1970- 0274029-X
    • (1970) Math. Comput. , vol.24 , pp. 647-656
    • Shanno, D.F.1
  • 47
    • 1942454763 scopus 로고    scopus 로고
    • The calculation of the vibrational frequencies of crystalline compounds and its implementation in the CRYSTAL code
    • 10.1002/jcc.20019
    • F. Pascale, C. M. Zicovich-Wilson, F. Liópez Gejo, B. Civalleri, R. Orlando, and R. Dovesi, " The calculation of the vibrational frequencies of crystalline compounds and its implementation in the CRYSTAL code," J. Comput. Chem. 25, 888-897 (2004). 10.1002/jcc.20019
    • (2004) J. Comput. Chem. , vol.25 , pp. 888-897
    • Pascale, F.1    Zicovich-Wilson, C.M.2    Liópez Gejo, F.3    Civalleri, B.4    Orlando, R.5    Dovesi, R.6
  • 48
    • 50149088807 scopus 로고    scopus 로고
    • The ab initio simulation of the IR spectra of Pyrope, Grossular and Andradite
    • 10.1002/jcc.20993
    • C. M. Zicovich-Wilson, J. Torres, F. Pascale, L. Valenzano, R. Orlando, and R. Dovesi, " The ab initio simulation of the IR spectra of Pyrope, Grossular and Andradite," J. Comput. Chem. 29, 2268-2278 (2008). 10.1002/jcc.20993
    • (2008) J. Comput. Chem. , vol.29 , pp. 2268-2278
    • Zicovich-Wilson, C.M.1    Torres, J.2    Pascale, F.3    Valenzano, L.4    Orlando, R.5    Dovesi, R.6
  • 49
    • 84870508359 scopus 로고    scopus 로고
    • Ab initio analytical infrared intensities for periodic systems through a coupled perturbed Hartree-Fock/Kohn-Sham method
    • 10.1063/1.4767438
    • L. Maschio, B. Kirtman, R. Orlando, and M. Rérat, " Ab initio analytical infrared intensities for periodic systems through a coupled perturbed Hartree-Fock/Kohn-Sham method," J. Chem. Phys. 137, 204113 (2012). 10.1063/1.4767438
    • (2012) J. Chem. Phys. , vol.137 , pp. 204113
    • Maschio, L.1    Kirtman, B.2    Orlando, R.3    Rérat, M.4
  • 50
    • 58149231183 scopus 로고    scopus 로고
    • Calculation of first and second static hyperpolarizabilities of one- to three-dimensional periodic compounds. Implementation in the CRYSTAL code
    • 10.1063/1.3043366
    • M. Ferrero, M. Rérat, B. Kirtman, and R. Dovesi, " Calculation of first and second static hyperpolarizabilities of one- to three-dimensional periodic compounds. Implementation in the CRYSTAL code," J. Chem. Phys. 129, 244110 (2008). 10.1063/1.3043366
    • (2008) J. Chem. Phys. , vol.129 , pp. 244110
    • Ferrero, M.1    Rérat, M.2    Kirtman, B.3    Dovesi, R.4
  • 51
    • 44449178442 scopus 로고    scopus 로고
    • The calculation of static polarizabilities of periodic compounds. The implementation in the CRYSTAL code for 1D, 2D and 3D systems
    • 10.1002/jcc.20905
    • M. Ferrero, M. Rérat, R. Orlando, and R. Dovesi, " The calculation of static polarizabilities of periodic compounds. The implementation in the CRYSTAL code for 1D, 2D and 3D systems," J. Comput. Chem. 29, 1450-1459 (2008). 10.1002/jcc.20905
    • (2008) J. Comput. Chem. , vol.29 , pp. 1450-1459
    • Ferrero, M.1    Rérat, M.2    Orlando, R.3    Dovesi, R.4
  • 55
    • 33644763018 scopus 로고    scopus 로고
    • Bilbao Crystallographic Server II: Representations of crystallographic point groups and space groups
    • 10.1107/S0108767305040286
    • M. I. Aroyo, A. Kirov, C. Capillas, J. M. Perez-Mato, and H. Wondratschek, " Bilbao Crystallographic Server II: Representations of crystallographic point groups and space groups," Acta Cryst. A 62, 115-128 (2006). 10.1107/S0108767305040286
    • (2006) Acta Cryst. A , vol.62 , pp. 115-128
    • Aroyo, M.I.1    Kirov, A.2    Capillas, C.3    Perez-Mato, J.M.4    Wondratschek, H.5
  • 56
    • 84899880949 scopus 로고    scopus 로고
    • See for Calcite animations.
    • See http://www.crystal.unito.it/vibs/carbonates/ for Calcite animations.
  • 57
    • 84899830019 scopus 로고    scopus 로고
    • See for Aragonite animations.
    • See http://www.crystal.unito.it/vibs/aragonite/ for Aragonite animations.
  • 58
    • 84899891739 scopus 로고    scopus 로고
    • See for Jmol 3d engine.
    • See http://jmol.sourceforge.net for Jmol 3d engine.
  • 59
    • 84899825481 scopus 로고    scopus 로고
    • See, for Jmoledit applet.
    • See http://www.theochem.unito.it/crystal-tuto/mssc2008-cd/tutorials/ webvib/index.html, for Jmoledit applet.
  • 60
    • 84899827610 scopus 로고    scopus 로고
    • See for Libreoffice suite.
    • See http://www.libreoffice.org for Libreoffice suite.
  • 61
    • 84899844511 scopus 로고    scopus 로고
    • See for Octave environment.
    • See http://www.gnu.org/software/octave for Octave environment.
  • 62
    • 84899875303 scopus 로고    scopus 로고
    • See for Gnuplot utility.
    • See http://www.gnuplot.info for Gnuplot utility.
  • 63
    • 55849088025 scopus 로고    scopus 로고
    • Evaluation of range-separated hybrid density functionals for the prediction of vibrational frequencies, infrared intensities, and Raman activities
    • 10.1039/b810877c
    • C. A. Jiménez-Hoyos, B. G. Janesko, and G. E. Scuseria, " Evaluation of range-separated hybrid density functionals for the prediction of vibrational frequencies, infrared intensities, and Raman activities," Phys. Chem. Chem. Phys. 10, 6621-6629 (2008). 10.1039/b810877c
    • (2008) Phys. Chem. Chem. Phys. , vol.10 , pp. 6621-6629
    • Jiménez-Hoyos, C.A.1    Janesko, B.G.2    Scuseria, G.E.3


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