This paper applies a density functional theory （DFT） and grand canonical Monte Carlo simulations （GCMC） to investigate the physisorptions of molecular hydrogen in single-walled BC3 nanotubes and carbon nanotubes. ...This paper applies a density functional theory （DFT） and grand canonical Monte Carlo simulations （GCMC） to investigate the physisorptions of molecular hydrogen in single-walled BC3 nanotubes and carbon nanotubes. The DFT calculations may provide useful information about the nature of hydrogen adsorption and physisorption energies in selected adsorption sites of these two nanotubes. Furthermore, the GCMC simulations can reproduce their storage capacity by calculating the weight percentage of the adsorbed molecular hydrogen under different conditions. The present results have shown that with both computational methods, the hydrogen storage capacity of BC3 nanotubes is superior to that of carbon nanotubes. The reasons causing different behaviour of hydrogen storage in these two nanotubes are explained by using their contour plots of electron density and charge-density difference.展开更多
NH_(3)-SCR脱硝技术由于其良好的脱硝效率及稳定性受到广泛应用,其核心是催化剂。γ-Fe_(2)O_(3)是一种具有良好低温脱硝活性的催化剂,采用Cu对其掺杂改性可有效提高其性能。为探究其反应机理,采用密度泛函理论(Density Function Theory...NH_(3)-SCR脱硝技术由于其良好的脱硝效率及稳定性受到广泛应用,其核心是催化剂。γ-Fe_(2)O_(3)是一种具有良好低温脱硝活性的催化剂,采用Cu对其掺杂改性可有效提高其性能。为探究其反应机理,采用密度泛函理论(Density Function Theory,DFT)方法对SCR反应过程中NH_(3)、NO、O_(2)等反应物分子在Cu掺杂γ-Fe_(2)O_(3)催化剂表面的吸附行为进行研究。结果表明,NH_(3)、NO、O_(2)均会吸附在Cu、Fe两个活性位点上,并形成稳定的吸附构型。在NH 3吸附过程中,NH_(3)会失去电子,N原子与Fe、Cu形成稳定的化学键。NO以N原子端靠近催化剂表面时,主要发生化学吸附,而以O原子靠近时发生物理吸附。NO主要表现为失去电子,当以N原子吸附时形成了稳定的化学键。O_(2)吸附时会得到电子并与金属离子之间形成稳定的化学吸附构型。在吸附过程中,小分子吸附于Fe活性位上时较为稳定。展开更多
Adsorption of CH3O at four sites （top, bridge, hcp, fcc） on Au（111） surface has been investigated by density functional theory method at the generalized gradient approximation level. We have performed calculations...Adsorption of CH3O at four sites （top, bridge, hcp, fcc） on Au（111） surface has been investigated by density functional theory method at the generalized gradient approximation level. We have performed calculations on adsorption energies, structures, Mulliken charges and vibrational frequencies of CH3O on Au（111） surface with full-geometry optimization. The predicted results are compared with the available experimental observation. The calculated CH3O adsorption structure and stretching vibrational frequencies agree well with experimental ones, and precise determinations of adsorption sites are carded out. The most favorite adsorption on Au（111） occurs at the bridge site, and O-C axis is tilted to the surface. However, on hollow sites （hcp, fcc） the species is adsorbed in an upright geometry （pseudo-C3v local symmetry）.展开更多
Cubic protactinium hydrides are very important existing form in superconducting protactinium hydrogen series. In this work, the ground state structure and properties of cubic PaH<sub>3</sub> have been stud...Cubic protactinium hydrides are very important existing form in superconducting protactinium hydrogen series. In this work, the ground state structure and properties of cubic PaH<sub>3</sub> have been studied using the DFT + U method. This systematic study for two bulk properties includes the electronic structures, phonon dispersion curves, structural, mechanical and thermodynamic properties under the effective coulomb U and exchange J PBE + U parameters. Structural relaxation results show that the Pa-H and Pa-Pa distances in α-PaH<sub>3</sub> are significantly higher than that in β-PaH<sub>3</sub>, and the H-H distances in α-PaH<sub>3</sub> are slightly smaller than that in β-PaH<sub>3</sub>. For the ground state electronic structures of α-PaH<sub>3</sub> and β-PaH<sub>3</sub>, we found that α-PaH<sub>3</sub> and β-PaH<sub>3</sub> are metallic, and the protactinium 5f electronic states and hydrogen have obvious bonding effect, resulting in weakening of the material’s metallicity. This is consistent with observations for the other actinide hydrides such as ThH<sub>3</sub> and UH<sub>3</sub>. The phonon spectrum calculations reveal that the PBE and PBE + U methods give quite different frequencies for the optical branches of phonons of α-PaH<sub>3</sub> and β-PaH<sub>3</sub>. In addition, by including the vibrational entropy and the ZPE using the phonon frequencies obtained from the optimized unit cells we predict that the β-PaH<sub>3</sub> phase can not transit into α-PaH<sub>3</sub> phase above room temperature.展开更多
DFT/6-311 + g** level calculations are performed tp study the electron transfer bond-breaking reaction of CH3-X. The calculated values are in good agreement with the experimental results or the empirical model. Throug...DFT/6-311 + g** level calculations are performed tp study the electron transfer bond-breaking reaction of CH3-X. The calculated values are in good agreement with the experimental results or the empirical model. Through analyzing the change of the energy and the charge densilty along hte reaction path, the bond-breaking in ET reaction for CH3X is investigated.展开更多
Accurate description of potential energy curves driven by nonbonded interactions remains a great challenge for pure density functional approximations(DFAs).It is because the Rdecay behavior of dispersion cannot be int...Accurate description of potential energy curves driven by nonbonded interactions remains a great challenge for pure density functional approximations(DFAs).It is because the Rdecay behavior of dispersion cannot be intrinsically captured by the(semi)-local ingredients and the exact-exchange used in the popular hybrid DFAs.Overemphasizing the accuracy on the equilibrium region for the functional construction would likely deteriorate the overall performance on the other regions of potential energy surfaces.In consequence,the empirical dispersion correction becomes the standard component in DFAs to treat the non-bonded interactions.In this Letter,we demonstrate that without the use of empirical dispersion correction,doubly hybrid approximations,in particular two recently proposed rev XYG3 and XYG7 functionals,hold the promise to have a balanced description of non-bonded interactions on the whole potential energy curves for several prototypes ofπ-π,CH/π,and SH/πinteractions.The error of rev XYG3 and XYG7 for non-bonded interactions is around 0.1 kcal/mol,and their potential energy curves almost coincide with the accurate CCSD(T)/CBS curves.展开更多
Third-order nonlinear optical (NLO) materials have broad application prospects in high-density data storage, optical computer, modern laser technology, and other high-tech industries. The structures and frequencies of...Third-order nonlinear optical (NLO) materials have broad application prospects in high-density data storage, optical computer, modern laser technology, and other high-tech industries. The structures and frequencies of Dinaphtho[2,3-b:2’,3’-d]thiophene-5,7,12,13-tetraone (DNTTRA) and its 36 derivatives containing azobenzene were calculated by using density functional theory B3LYP and M06-2X methods at 6-311++g(d, p) level, respectively. Besides, the atomic charges of natural bond orbitals (NBO) were analyzed. The frontier orbitals and electron absorption spectra of A-G5 molecule were calculated by TD-DFT (TD-B3LYP/6-311++g(d, p) and TD-M06-2X/6-311++g(d, p)). The NLO properties were calculated by effective finite field FF method and self-compiled program. The results show that 36 molecules of these six series are D-π-A-π-D structures. The third-order NLO coefficients γ (second-order hyperpolarizability) of the D series molecules are the largest among the six series, reaching 10<sup>7</sup> atomic units (10<sup><span style="color:#4F4F4F;font-family:-apple-system, " font-size:14px;white-space:normal;background-color:#ffffff;"="">-</span>33</sup> esu) of order of magnitude, showing good third-order NLO properties. Last, the third-order NLO properties of the azobenzene ring can be improved by introducing strong electron donor groups (e.g. -N(CH<sub>3</sub>)<sub>2</sub> or -NHCH<sub>3</sub>) in the azobenzene ring, so that the third-order NLO materials with good performance can be obtained.展开更多
1,2-Benzothiazine derivatives methyl 3-methoxy-4-oxo-3,4-dihydro-2H-benzo[e] [1,2]thiazine-3-carboxylate 1,1-dioxide（1） and methyl 2-ethyl-3-hydroxy-4-oxo-3,4-dihydro-2Hbenzo[e][1,2]thiazine-3-carboxylate 1,1-dioxid...1,2-Benzothiazine derivatives methyl 3-methoxy-4-oxo-3,4-dihydro-2H-benzo[e] [1,2]thiazine-3-carboxylate 1,1-dioxide（1） and methyl 2-ethyl-3-hydroxy-4-oxo-3,4-dihydro-2Hbenzo[e][1,2]thiazine-3-carboxylate 1,1-dioxide（2） were synthesized, and characterized by spectroscopic techniques; 1H-NMR and infrared（IR） spectroscopy. Crystals of 1 and 2 were grown by slow evaporation of methanol and ethyl acetate, respectively and their crystal structures were investigated by single-crystal X-ray diffraction analysis. Geometric properties were calculated by the B3 LYP method of density functional theory（DFT） at the 6-31G＋（d） basis set to compare with the experimental data. Simulated properties were found in strong agreement with the experimental ones. Intermolecular forces have also been modeled in order to investigate the strength of packing and strong hydrogen bonding was observed in both compounds 1 and 2. Electronic properties such as Ionization Potential（IP）, Electron Affinities（EA） and coefficients of the highest occupied molecular orbital（HOMO） and the lowest unoccupied molecular orbital（LUMO） of com- pounds 1 and 2 were simulated for the first time.展开更多
By means of density functional calculations, the structural and electronic properties of chemical modification of pristine and Ca-doped BeO nanotubes were investigated with NH3 and H20 molecules. It was found that the...By means of density functional calculations, the structural and electronic properties of chemical modification of pristine and Ca-doped BeO nanotubes were investigated with NH3 and H20 molecules. It was found that the NH3 and H20 molecules can be adsorbed on the Be atom of the tube sidewall with the adsorption energies of about 36.1 and 39.0 kcal/mol, respectively. Density of states analysis shows that the electronic properties of the BeONT are slightly changed after the adsorption processes. Substitution of a Be atom in the tube surface with a Ca atom increases the adsorption energies by about 7.4 and 14.7 kcal/mol for NH3 and H20, respectively. Unlike the pristine tube, the electronic properties of Ca-doped BeONT are sensitive to NH3 and H20 molecules. Also, the Ca-doped tube is much more sensitive to H20 molecule than NH3 one.展开更多
The electronic structures, Born effective charges（BECs）, and full phonon dispersions of cubic, tetragonal, orthorhombic, and rhombohedral K0.5Na0.5Nb O3 are investigated by the first principles method based on densi...The electronic structures, Born effective charges（BECs）, and full phonon dispersions of cubic, tetragonal, orthorhombic, and rhombohedral K0.5Na0.5Nb O3 are investigated by the first principles method based on density functional theory.The hybridized states of Nb 4d and O 2p states are observed in the valence band, showing the formation of a strong Nb–O covalent bond which should be responsible for the displacement of Nb and O atoms. The abnormally large BECs of Nb and O indicate the possibility of phase instability induced by the off-center displacement of Nb and O atoms. The phonon dispersions reveal that the ferroelectric instability of K0.5Na0.5Nb O3 is dominated by Nb and O displacements with significant Na characteristics. In addition to the ferroelectric instability, there is also rotational instability coming from the oxygen octahedra rotation around one axis. Moreover, the Γ phonon properties of orthorhombic KNb O3, Na Nb O3, and K0.5Na0.5Nb O3 are also studied in detail.展开更多
First principle calculation within the Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT) using Local Density Approximation as implemented in Quantum ESPRESSO has been significantly used...First principle calculation within the Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT) using Local Density Approximation as implemented in Quantum ESPRESSO has been significantly used to investigate the structural and Piezoelectric, properties of Perovskite ZrTi(PbO3)2. From structural properties calculation, the ground state total energy of -2417.12 eV has been obtained which led to an equilibrium lattice constant of a= 5.620Åfor ZrTi(PbO3)2. Our obtained optimized atomic positions and atomic effective charge shows that the optimized ZrTi(PbO3)2 is stable and the Piezoelectric stress tensor is calculated using Berry-phase approach within density functional perturbation theory (DFPT). From our calculation, we have obtained the stress tensor elements with values of d1,5 = 6.81, d3,1 = 1.69, and d3,3 = 6.18, which is in agreement with the values obtained for tetragonal PbTiO3.展开更多
Geometry optimization at the B3LYP/6-31＋＋G＊ level of theory has been undertaken on clusters containing L-Met （L-methionine） or L-Cys （L-cysteine） surrounded by eight water molecules. The comparison of the struc...Geometry optimization at the B3LYP/6-31＋＋G＊ level of theory has been undertaken on clusters containing L-Met （L-methionine） or L-Cys （L-cysteine） surrounded by eight water molecules. The comparison of the structural parameters of L-Met and L-Cys with X-ray experimental values is in good agreement within 4.8%. This result shows that the privileged positions of water molecules and the possible hydrogen bonding network formed around the backbone of both AAs （amino acids） are adequate. Subsequent calculations of the harmonic vibrational modes followed by a post-processing treatment enable us to assign the vibrational modes of L-Met and L-Cys surrounded explicitly by eight water molecules. The frequencies of the assigned modes are in good agreement with available IR （infra red） and Raman values within 5%.展开更多
基金Project supported by Henan University of Technology Foundation (Grant No. 2009BS025)China Academy of Engineering Physics Foundation (Grant No. 2007B08008)
文摘This paper applies a density functional theory （DFT） and grand canonical Monte Carlo simulations （GCMC） to investigate the physisorptions of molecular hydrogen in single-walled BC3 nanotubes and carbon nanotubes. The DFT calculations may provide useful information about the nature of hydrogen adsorption and physisorption energies in selected adsorption sites of these two nanotubes. Furthermore, the GCMC simulations can reproduce their storage capacity by calculating the weight percentage of the adsorbed molecular hydrogen under different conditions. The present results have shown that with both computational methods, the hydrogen storage capacity of BC3 nanotubes is superior to that of carbon nanotubes. The reasons causing different behaviour of hydrogen storage in these two nanotubes are explained by using their contour plots of electron density and charge-density difference.
文摘NH_(3)-SCR脱硝技术由于其良好的脱硝效率及稳定性受到广泛应用,其核心是催化剂。γ-Fe_(2)O_(3)是一种具有良好低温脱硝活性的催化剂,采用Cu对其掺杂改性可有效提高其性能。为探究其反应机理,采用密度泛函理论(Density Function Theory,DFT)方法对SCR反应过程中NH_(3)、NO、O_(2)等反应物分子在Cu掺杂γ-Fe_(2)O_(3)催化剂表面的吸附行为进行研究。结果表明,NH_(3)、NO、O_(2)均会吸附在Cu、Fe两个活性位点上,并形成稳定的吸附构型。在NH 3吸附过程中,NH_(3)会失去电子,N原子与Fe、Cu形成稳定的化学键。NO以N原子端靠近催化剂表面时,主要发生化学吸附,而以O原子靠近时发生物理吸附。NO主要表现为失去电子,当以N原子吸附时形成了稳定的化学键。O_(2)吸附时会得到电子并与金属离子之间形成稳定的化学吸附构型。在吸附过程中,小分子吸附于Fe活性位上时较为稳定。
文摘Adsorption of CH3O at four sites （top, bridge, hcp, fcc） on Au（111） surface has been investigated by density functional theory method at the generalized gradient approximation level. We have performed calculations on adsorption energies, structures, Mulliken charges and vibrational frequencies of CH3O on Au（111） surface with full-geometry optimization. The predicted results are compared with the available experimental observation. The calculated CH3O adsorption structure and stretching vibrational frequencies agree well with experimental ones, and precise determinations of adsorption sites are carded out. The most favorite adsorption on Au（111） occurs at the bridge site, and O-C axis is tilted to the surface. However, on hollow sites （hcp, fcc） the species is adsorbed in an upright geometry （pseudo-C3v local symmetry）.
文摘Cubic protactinium hydrides are very important existing form in superconducting protactinium hydrogen series. In this work, the ground state structure and properties of cubic PaH<sub>3</sub> have been studied using the DFT + U method. This systematic study for two bulk properties includes the electronic structures, phonon dispersion curves, structural, mechanical and thermodynamic properties under the effective coulomb U and exchange J PBE + U parameters. Structural relaxation results show that the Pa-H and Pa-Pa distances in α-PaH<sub>3</sub> are significantly higher than that in β-PaH<sub>3</sub>, and the H-H distances in α-PaH<sub>3</sub> are slightly smaller than that in β-PaH<sub>3</sub>. For the ground state electronic structures of α-PaH<sub>3</sub> and β-PaH<sub>3</sub>, we found that α-PaH<sub>3</sub> and β-PaH<sub>3</sub> are metallic, and the protactinium 5f electronic states and hydrogen have obvious bonding effect, resulting in weakening of the material’s metallicity. This is consistent with observations for the other actinide hydrides such as ThH<sub>3</sub> and UH<sub>3</sub>. The phonon spectrum calculations reveal that the PBE and PBE + U methods give quite different frequencies for the optical branches of phonons of α-PaH<sub>3</sub> and β-PaH<sub>3</sub>. In addition, by including the vibrational entropy and the ZPE using the phonon frequencies obtained from the optimized unit cells we predict that the β-PaH<sub>3</sub> phase can not transit into α-PaH<sub>3</sub> phase above room temperature.
文摘DFT/6-311 + g** level calculations are performed tp study the electron transfer bond-breaking reaction of CH3-X. The calculated values are in good agreement with the experimental results or the empirical model. Through analyzing the change of the energy and the charge densilty along hte reaction path, the bond-breaking in ET reaction for CH3X is investigated.
基金supported by the National Natural Science Foundation of China(No.21973015,No.22125301,No.91427301)the Science Challenge Project(TZ2018004)+1 种基金Innovative Research Team of High-Level Local universities in Shanghaia Key Laboratory Program of the Education Commission of Shanghai Municipality(ZDSYS14005)。
文摘Accurate description of potential energy curves driven by nonbonded interactions remains a great challenge for pure density functional approximations(DFAs).It is because the Rdecay behavior of dispersion cannot be intrinsically captured by the(semi)-local ingredients and the exact-exchange used in the popular hybrid DFAs.Overemphasizing the accuracy on the equilibrium region for the functional construction would likely deteriorate the overall performance on the other regions of potential energy surfaces.In consequence,the empirical dispersion correction becomes the standard component in DFAs to treat the non-bonded interactions.In this Letter,we demonstrate that without the use of empirical dispersion correction,doubly hybrid approximations,in particular two recently proposed rev XYG3 and XYG7 functionals,hold the promise to have a balanced description of non-bonded interactions on the whole potential energy curves for several prototypes ofπ-π,CH/π,and SH/πinteractions.The error of rev XYG3 and XYG7 for non-bonded interactions is around 0.1 kcal/mol,and their potential energy curves almost coincide with the accurate CCSD(T)/CBS curves.
文摘Third-order nonlinear optical (NLO) materials have broad application prospects in high-density data storage, optical computer, modern laser technology, and other high-tech industries. The structures and frequencies of Dinaphtho[2,3-b:2’,3’-d]thiophene-5,7,12,13-tetraone (DNTTRA) and its 36 derivatives containing azobenzene were calculated by using density functional theory B3LYP and M06-2X methods at 6-311++g(d, p) level, respectively. Besides, the atomic charges of natural bond orbitals (NBO) were analyzed. The frontier orbitals and electron absorption spectra of A-G5 molecule were calculated by TD-DFT (TD-B3LYP/6-311++g(d, p) and TD-M06-2X/6-311++g(d, p)). The NLO properties were calculated by effective finite field FF method and self-compiled program. The results show that 36 molecules of these six series are D-π-A-π-D structures. The third-order NLO coefficients γ (second-order hyperpolarizability) of the D series molecules are the largest among the six series, reaching 10<sup>7</sup> atomic units (10<sup><span style="color:#4F4F4F;font-family:-apple-system, " font-size:14px;white-space:normal;background-color:#ffffff;"="">-</span>33</sup> esu) of order of magnitude, showing good third-order NLO properties. Last, the third-order NLO properties of the azobenzene ring can be improved by introducing strong electron donor groups (e.g. -N(CH<sub>3</sub>)<sub>2</sub> or -NHCH<sub>3</sub>) in the azobenzene ring, so that the third-order NLO materials with good performance can be obtained.
基金funded by the Saudi Basic Industries Corporation(SABIC) and the Deanship of Scientific Research(DSR),King Abdulaziz University,Jeddah,under grant no.(MS/15/396/1434)
文摘1,2-Benzothiazine derivatives methyl 3-methoxy-4-oxo-3,4-dihydro-2H-benzo[e] [1,2]thiazine-3-carboxylate 1,1-dioxide（1） and methyl 2-ethyl-3-hydroxy-4-oxo-3,4-dihydro-2Hbenzo[e][1,2]thiazine-3-carboxylate 1,1-dioxide（2） were synthesized, and characterized by spectroscopic techniques; 1H-NMR and infrared（IR） spectroscopy. Crystals of 1 and 2 were grown by slow evaporation of methanol and ethyl acetate, respectively and their crystal structures were investigated by single-crystal X-ray diffraction analysis. Geometric properties were calculated by the B3 LYP method of density functional theory（DFT） at the 6-31G＋（d） basis set to compare with the experimental data. Simulated properties were found in strong agreement with the experimental ones. Intermolecular forces have also been modeled in order to investigate the strength of packing and strong hydrogen bonding was observed in both compounds 1 and 2. Electronic properties such as Ionization Potential（IP）, Electron Affinities（EA） and coefficients of the highest occupied molecular orbital（HOMO） and the lowest unoccupied molecular orbital（LUMO） of com- pounds 1 and 2 were simulated for the first time.
文摘By means of density functional calculations, the structural and electronic properties of chemical modification of pristine and Ca-doped BeO nanotubes were investigated with NH3 and H20 molecules. It was found that the NH3 and H20 molecules can be adsorbed on the Be atom of the tube sidewall with the adsorption energies of about 36.1 and 39.0 kcal/mol, respectively. Density of states analysis shows that the electronic properties of the BeONT are slightly changed after the adsorption processes. Substitution of a Be atom in the tube surface with a Ca atom increases the adsorption energies by about 7.4 and 14.7 kcal/mol for NH3 and H20, respectively. Unlike the pristine tube, the electronic properties of Ca-doped BeONT are sensitive to NH3 and H20 molecules. Also, the Ca-doped tube is much more sensitive to H20 molecule than NH3 one.
基金Project supported by the Jiangxi Provincial Natural Science Foundation,China(Grant No.20122BAB216007)the Foundation of Jiangxi Provincial Educational Committee,China(Grant No.GJJ14648)
文摘The electronic structures, Born effective charges（BECs）, and full phonon dispersions of cubic, tetragonal, orthorhombic, and rhombohedral K0.5Na0.5Nb O3 are investigated by the first principles method based on density functional theory.The hybridized states of Nb 4d and O 2p states are observed in the valence band, showing the formation of a strong Nb–O covalent bond which should be responsible for the displacement of Nb and O atoms. The abnormally large BECs of Nb and O indicate the possibility of phase instability induced by the off-center displacement of Nb and O atoms. The phonon dispersions reveal that the ferroelectric instability of K0.5Na0.5Nb O3 is dominated by Nb and O displacements with significant Na characteristics. In addition to the ferroelectric instability, there is also rotational instability coming from the oxygen octahedra rotation around one axis. Moreover, the Γ phonon properties of orthorhombic KNb O3, Na Nb O3, and K0.5Na0.5Nb O3 are also studied in detail.
文摘First principle calculation within the Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT) using Local Density Approximation as implemented in Quantum ESPRESSO has been significantly used to investigate the structural and Piezoelectric, properties of Perovskite ZrTi(PbO3)2. From structural properties calculation, the ground state total energy of -2417.12 eV has been obtained which led to an equilibrium lattice constant of a= 5.620Åfor ZrTi(PbO3)2. Our obtained optimized atomic positions and atomic effective charge shows that the optimized ZrTi(PbO3)2 is stable and the Piezoelectric stress tensor is calculated using Berry-phase approach within density functional perturbation theory (DFPT). From our calculation, we have obtained the stress tensor elements with values of d1,5 = 6.81, d3,1 = 1.69, and d3,3 = 6.18, which is in agreement with the values obtained for tetragonal PbTiO3.
文摘Geometry optimization at the B3LYP/6-31＋＋G＊ level of theory has been undertaken on clusters containing L-Met （L-methionine） or L-Cys （L-cysteine） surrounded by eight water molecules. The comparison of the structural parameters of L-Met and L-Cys with X-ray experimental values is in good agreement within 4.8%. This result shows that the privileged positions of water molecules and the possible hydrogen bonding network formed around the backbone of both AAs （amino acids） are adequate. Subsequent calculations of the harmonic vibrational modes followed by a post-processing treatment enable us to assign the vibrational modes of L-Met and L-Cys surrounded explicitly by eight water molecules. The frequencies of the assigned modes are in good agreement with available IR （infra red） and Raman values within 5%.
