Geometry Optimization Calculations Research Articles

Synthesis, crystal structure, DFT calculations and Hirshfeld surface analysis of 3-butyl-2,6-bis-(4-fluoro-phen-yl)piperidin-4-one.

The title compound, C21H23F2NO, consists of two fluoro-phenyl groups and one butyl group equatorially oriented on a piperidine ring, which adopts a chair conformation. The dihedral angle between the mean planes of the phenyl rings is 72.1 (1)°. In the crystal, N-H⋯O and weak C-H⋯F inter-actions, which form R 2 2[14] motifs, link the mol-ecules into infinite C(6) chains propagating along [001]. A weak C-H⋯π inter-action is also observed. A Hirshfeld surface analysis of the crystal structure indicates that the most significant contributions to the crystal packing are from H⋯H (53.3%), H⋯C/C⋯H (19.1%), H⋯F/F⋯H (15.7%) and H⋯O/O⋯H (7.7%) contacts. Density functional theory geometry-optimized calculations were compared to the experimentally determined structure in the solid state and used to determine the HOMO-LUMO energy gap and compare it to the UV-vis experimental spectrum.

Theoretical investigation of structural and magnetic properties of MnTiX (X = Si, Ge, Se, Te) half-Heusler alloys

The structural, electronic, and magnetic properties of half-Heusler alloys (HHAs) MnTiX (X = Si, Ge, Se, Te) are studied using full potential linearized augmented plane wave (FP-LAPW) method as implemented in Wien2k code which is a well-known code to investigate the physical properties of materials. The geometry optimization calculations for ferromagnetic (FM) and anti-ferromagnetic phases have been performed in order to determine the most stable phase of these materials. The results revealed that FM phase is the most stable, and further calculations (spin band structures and density of states) are carried for FM phase. The obtained results of band structures and density of states show that all considered alloys have half-metallic (HM) behavior with 100% spin polarization at the Fermi level. Furthermore, the exchange coupling of s-d and p-d exchange have also been discussed in detail for these materials.

A theoretical study of X‐H∙∙∙π and X∙∙∙π interactions in the complexes of furan, thiophene, pyrrole and hydrogen halides

AbstractBy using ab initio geometry optimization calculations we obtained thirteen stable complexes containing H∙∙∙π and X∙∙∙π interactions between Furan, Thiophene, Pyrrole and HX (X = F, Cl, Br) at the MP2/6‐311++G(3df,2pd) high level of theory. The interaction energies corrected for only ZPE and both ZPE and BSSE range from ‐7.92 to ‐28.47 kJ.mol‐1 and ‐3.28 to ‐22.33 kJ.mol‐1, respectively. The results show that for the same HX, the stability of complexes decreases in going from Pyrrole to Thiophene and finally to Furan moiety, and increases in the order of HF < HCl < HBr monomer with the same π‐system. The obtained results from AIM and MEP analyses indicate that the H∙∙∙π interaction is more stable than X∙∙∙π one in all the investigated complexes. It is found that the electrostatic, dispersion and induction energy terms significantly contribute to strength of the studied complexes, in which two formers are for H∙∙∙π hydrogen bonded complexes and two latters are for X∙∙∙π halogen bonded complexes.

Machine learning the computational cost of quantum chemistry

Computational quantum mechanics based molecular and materials design campaigns consume increasingly more high-performance computer resources, making improved job scheduling efficiency desirable in order to reduce carbon footprint or wasteful spending. We introduce quantum machine learning (QML) models of the computational cost of common quantum chemistry tasks. For 2D nonlinear toy systems, single point, geometry optimization, and transition state calculations the out of sample prediction error of QML models of wall times decays systematically with training set size. We present numerical evidence for a toy system containing two functions and three commonly used optimizer and for thousands of organic molecular systems including closed and open shell equilibrium structures, as well as transition states. Levels of electronic structure theory considered include B3LYP/def2-TZVP, MP2/6-311G(d), local CCSD(T)/VTZ-F12, CASSCF/VDZ-F12, and MRCISD+Q-F12/VDZ-F12. In comparison to conventional indiscriminate job treatment, QML based wall time predictions significantly improve job scheduling efficiency for all tasks after training on just thousands of molecules. Resulting reductions in CPU time overhead range from 10% to 90%.

Theoretical investigation on the spectroscopic properties and catalytic activities of the Ti-Hydroperoxo intermediates in titanosilicate zeolites

Abstract The spectroscopic features of the Ti-hydroperoxo intermediates in TS-1, Ti-BEA, and Ti-YNU-1 zeolites were studied by using theoretical calculations. The Ti-hydroperoxo intermediates, Ti-η1(OOH), Ti-η1(OOH)–H2O, Ti-η2(OOH), and Ti-η2(OOH)–H2O species, as well as Ti-η1(OOH)–CH3OH, Ti-η1(OOH)–CH3CN, Ti-η2(OOH)–CH3OH, and Ti-η2(OOH)–CH3CN species were constructed and their IR, Raman, and UV–vis spectra were calculated. The geometry optimization and vibrational frequency calculations were carried out with DFT method at the theoretical level of B3LYP/6-31G(d, p), and the UV–vis spectra were obtained with TD-DFT method at the theoretical level of PBEPBE/6–311++G(d, p). The calculated structures show the average Ti–O bond distances of 2.01 ± 0.02 A, consistent well with the experimental EXAFS data reported in the literatures. The calculated IR and Raman spectra of Ti-hydroperoxo intermediates show that the Oα–Oβ stretching vibrations are in the range of 870–910 cm−1 for Ti-η1(OOH) and Ti-η1(OOH)-R (R = H2O, CH3OH, CH3CN) species, and 834–855 cm−1 for Ti-η2(OOH) and Ti-η2(OOH)-R species. TD-DFT calculations indicate that for Ti-η1(OOH) and Ti-η1(OOH)-R species, the transition wavelengths are in the range of 350–365 nm and 370–400 nm, respectively, which are ascribed to the electron transition from the p orbital of the active oxygen Oα and Oβ to the unoccupied d* orbital of framework Ti atom, being responsible for the 385 nm band observed in the experimental UV–vis spectrum of TS-1 zeolite as contacting with H2O2 aqueous solution. Whereas, for the Ti-η2(OOH) and Ti-η2(OOH)-R species, all the corresponding transitions are below 350 nm. The catalytic performances of the Ti-hydroperoxo intermediates for olefin epoxidation were also evaluated. In combination of the calculated geometric parameters, the stabilities, the spectroscopic properties, and the catalytic performances, it is demonstrated that the initially formed Ti-hydroperoxo intermediates in titanosilicate/H2O2/H2O system should be Ti-η1(OOH)–H2O or Ti-η1(OOH) species, which then converts into the more stable Ti-η2(OOH)–H2O species that works as the actual catalytic active center for epoxidation reactions. If the solvent is methanol or acetonitrile, Ti-η2(OOH)–CH3OH or Ti-η2(OOH)–CH3CN species should be the predominant active center.

Computational Study of Anthocyanin as Active Material in Dye-Sensitized Solar Cell

Computational calculations for anthocyanin (anthocyanidin-3-monoglucoside) compounds were performed to get structure and electronic properties from the three of anthocyanin which has potential as active material in the dye-sensitized solar cell. The calculations use Density Functional Theory (DFT) with B3LYP functional and 6-31G(d) for ground state geometry optimization and Time Dependent-Density Functional Theory (TD-DFT) for excited states single point calculation. All the calculations were conducted in the gas phase. Geometry optimization calculations show that structures of anthocyanin compounds are not planar. Single point calculation for excited states shows absorption wavelength is shorter than experimental data, with a difference between 7.3% to 8.3%. The density of HOMO-LUMO is spread only on anthocyanidin part. The LUMO density of the three compounds is mostly in the anchoring group. In terms of excitation energy from the composition of excitation and distribution of HOMO-LUMO, cyanidin-3-monoglucoside shows better potency as active material in dye-sensitized solar cells.

Using Atomic Confining Potentials for Geometry Optimization and Vibrational Frequency Calculations in Quantum-Chemical Models of Enzyme Active Sites.

Quantum-chemical studies of enzymatic reaction mechanisms sometimes use truncated active-site models as simplified alternatives to mixed quantum mechanics molecular mechanics (QM/MM) procedures. Eliminating the MM degrees of freedom reduces the complexity of the sampling problem, but the trade-off is the need to introduce geometric constraints in order to prevent structural collapse of the model system during geometry optimizations that do not contain a full protein backbone. These constraints may impair the efficiency of the optimization, and care must be taken to avoid artifacts such as imaginary vibrational frequencies. We introduce a simple alternative in which terminal atoms of the model system are placed in soft harmonic confining potentials rather than being rigidly constrained. This modification is simple to implement and straightforward to use in vibrational frequency calculations, unlike iterative constraint-satisfaction algorithms, and allows the optimization to proceed without constraint even though the practical result is to fix the anchor atoms in space. The new approach is more efficient for optimizing minima and transition states, as compared to the use of fixed-atom constraints, and also more robust against unwanted imaginary frequencies. We illustrate the method by application to several enzymatic reaction pathways where entropy makes a significant contribution to the relevant reaction barriers. The use of confining potentials correctly describes reaction paths and facilitates calculation of both vibrational zero-point and finite-temperature entropic corrections to barrier heights.

Theoretical studies of squaraine and functionalized 2,1,3-benzothiadiazole molecules for solar cell applications

Research on alternative renewable energy sources is of great interest because of increasing world energy demand and depleting non-renewable energy resources. Both organic and inorganic solar cells are an important category of alternative energy resources. Inorganic solar cells, being the most successful technology has demerits such as high cost, rigidity etc. Organic solar cell is a better alternative with power conversion efficiency more than 17%. Squaraine is an important class of electron donating compounds which has high absorption and emission in the visible to near IR region. Organic photovoltaic devices with squaraine-fullerene systems attained 8% power conversion efficiency, which denotes that squaraine compounds have the potential for future organic solar cells. Organic materials consisting of 2,1,3-benzothiadiazole as core functionalized with different chromophore and squaraine as arms and vice versa may be a potential molecule for the fabrication of various organic electronic devices. By understanding the band gap, excitation energies and light-harvesting capability the designed molecules can be effectively used in solar cell applications. Here we designed and studied different squaraine containing molecules whose geometry optimization and band gap calculations are done by time-dependent DFT method.

A theoretical study of the addition of CH2OO to hydroxymethyl hydroperoxide and its implications on SO3 formation in the atmosphere.

The reaction of hydroxymethyl hydroperoxide (HMHP, HOCH2OOH) with the simplest Criegee intermediate, CH2OO, has been examined using quantum chemical methods with transition state theory. Geometry optimization and IRC calculations were performed using the M06-2X, MN15-L, and B2PLYP-D3 functionals in conjunction with the aug-cc-pVTZ basis set. Single point energy calculations using QCISD(T) and BD(T) with the same basis set have been performed to determine the energy of reactants, reactive complexes, transition states, and products. Rate coefficients have been obtained using variational transition state theory. The addition of CH2OO on the three different oxygen atoms in HMHP has been considered and the ether oxide forming channel, CH2OO + HOCH2OOH → HOCH2O(O)CH2OOH (channel 2), is the most favorable. The best computed standard enthalpy of reaction (ΔH) and zero-point corrected barrier height are -20.02 and -6.33 kcal mol-1, respectively. The reaction barrier is negative and our results suggest that both the inner and outer transition states contribute to the corresponding overall reactive flux in the tropospheric temperature range (220 K to 320 K). A two-transition state model has been used to obtain reliable rate coefficients at the high-pressure limit. The pressure-dependent rate coefficient calculations using the SS-QRRK theory have shown that this channel is pressure-dependent. Moreover, our investigation has shown that the ether oxide formed may rapidly react with SO2 at 298 K to form SO3, which can, in turn, react with water to form atmospheric H2SO4. A similar calculation has been conducted for the reaction of HMHP with OH, suggesting that the titled reaction may be a significant sink of HMHP. Therefore, the reaction between CH2OO and HOCH2OOH could be an indirect source for generating atmospheric H2SO4, which is crucial to the formation of clouds, and it might relieve global warming.

Modelling of the Elementary Steps Involved in the Aluminum Electrochemical Deposition from Ionic Liquid Based Solution: The BMImCl/AlCl3 System

The energy hierarchy, of the main chemical species involved in the reaction mechanism relevant to the electrodeposition of aluminum in 1-Butyl-3-methylimidazolium chloride/aluminum trichloride solution (BMImCl/AlCl3), is studied by using ab-initio based theoretical calculations. Eventually, a reasonable theoretical estimate of energies, involved in the principal reactions ruling the aluminum electrodeposition from BMImCl ionic liquid solutions, is obtained. For screening purposes (geometry optimization and Hessian calculations) the CAMB3LYP density functional, DFT, has been used. Then single point (exploiting CAMB3LYP optimized geometries) energy data are obtained at the Møller-Plesset (MP2) level of the theory. They are used to cross-check DFT results. A reaction mechanism emerges in which, although the species AlCl−4 is formed with very high efficiency from the neutral species AlCl3, the competing reaction points to an almost complete conversion of aluminum to the dimeric form into bulk solution. This is observed in the absence and, most importantly, in the presence of a coordinating BMIm+ cation. In this respect, the presence of BMIm+ does not seem to affect significantly the equilibrium between the monomeric and dimeric forms of aluminum. This outcome is very interesting because the dimeric species is directly reduced to yield the metal aluminum. Indeed, a larger concentration of Al2Cl−7 gives due reason for a more effective electrodeposition process, as it is experimentally observed in the ionic liquid medium.

CO2 Capture with Silylated Ethanolamines and Piperazines.

Amine treatment is commonly used to capture CO2 from exhaust gases and from ambient air. The Si−N bond in aminosilanes is capable of reacting with CO2 more readily than amines. In the current study we have synthesized trimethylsilylated ethanolamines, diethanolamines and piperazines and investigated their reaction toward CO2. All products were characterized by 1H, 13C, and 29Si NMR, RAMAN spectroscopy as well as mass spectrometry. The product of a twofold CO2‐insertion into bis‐trimethylsilylated piperazine was analysed by single‐crystal X‐ray diffraction. Furthermore, quantum chemical calculations (DFT) were used to supplement the experimental results. Geometry optimizations and NBO calculations for each starting material were carried out at the B3LYP level with different basis sets. DFT calculations at the B3LYP, WB97XD and M062x level were conducted for geometry optimization and frequency calculations to examine the thermochemical data. The calculations were carried out both for the gas phase and in solvent environment. The calculated reaction enthalpies varied between −37 and −107 kJ mol−1, while experimental values around −100 kJ mol−1 were determined.

Synthesis, Crystal Structures, Density Functional Theory (DFT) Calculations and Molecular Orbital Calculations of Two New Metal-Free Macrocyclic Schiff Bases Derived from 2,6-Dibenzoyl-4-alkylphenol and Diamines

Two new phenol-based metal-free macrocyclic Schiff bases, cyclo-bis{2-[benz(N-propan-1,3-diyl)imidoyl][6-benzimidoyl][4-methyl]phenol} and cyclo-bis{2-[benz(N-butan-1,4-diyl)imidoyl][6-benzimidoyl][4-tert-butyl]phenol} have been synthesized and their structures determined by single crystal X-ray crystallography. The DFT geometry optimization calculations were performed to compare experimental and theoretical results. A comparison of the dihedral angles between mean planes of the central phenolato rings and peripheral phenyl rings in the crystal with the DFT theoretical calculations has been included for each molecule. Electronic transitions have been predicted by DFT molecular orbital calculations and compared with experimental absorption spectral data. A one-pot synthesis, crystal structure and theoretical calculations of 20- and 22-membered macrocyclic ligands are reported.

Theoretical investigations of the structural and electronic properties of boron nitride clusters: DFT comparison of several basis sets

In this present study, Density Functional Theory (DFT) calculations were conducted to study the structural and electronic properties of (1,1), (2,2), (3,3), and (4,4) Boron Nitride (BN) systems. Geometry optimization calculations were carried out to find the stability of BN cluster models. The obtained structural geometries are consistent with that obtained in the previous reported results [1]. The total energies increase when the cluster sizes of BNs increase. For each cluster size of BN, the four total energy values obtained from B3LYP level of theory with employing the basis sets of 6-31++G, 6-31++G**, 6-311++G, and 6-311++G** are close to each. Moreover, our computations revealed that the gap energy values of HOMO-LUMOs in the BN cluster structures have been decreased by following its structure and dimensionality. The calculated HOMO-LUMO gaps are 5.99 eV - 7.68 eV in this study. For the diagrams of molecular electrostatic potential (MEP) surfaces, the regions around the N atoms at the center hold the highest electronegative potential, which can attract more electrons in the BN systems. With a Mulliken population analysis (MPA) scheme, all the boron atoms possess the positive charges, whereas the negative charges were found on the nitrogen atom in the BN systems.

Prediction of octanol-air partition coefficients for PCBs at different ambient temperatures based on the solvation free energy and the dimer ratio.

Temperature-dependent octanol-air partition coefficients (KOA) are of great importance in assessing the environmental behavior and fate of persistent organic pollutants including polychlorinated biphenyls (PCBs). Due to the tremendous amounts of time, effort and cost needed for the experimental determination of KOA, it is desirable to develop a rapid and precise predictive method to estimate KOA just based on molecular structure. In the present study, a predictive model for log KOA of PCBs at ambient temperatures was developed based on the thermodynamic relationship between KOA and the solvation free energy from air to octanol (ΔGOA). For the calculation of ΔGOA of PCBs, the optimal combination of theoretical method and basis-set was identified to be HF/MIDI!6D for both geometry optimization and energy calculation. Dimer formation could affect the partition behavior and promote the apparent KOA values of PCBs. After taking the effect of dimer formation into account, the goodness-of-fit, predictive ability, and robustness of the predictive model were significantly improved. Apparent log KOA values of PCBs at different ambient temperatures ranging from 283.15 to 303.15 K were predicted. Compared with other reported models, the model developed in the present study had not only comparable goodness-of-fit and predictive ability, but also a universal application domain and the relative independency of experimental data. Therefore, the solvation free energy method could be a promising method for the prediction of KOA.

Predicting the degradation potential of Acid blue 113 by different oxidants using quantum chemical analysis

In this work, quantum chemical analysis was used to predict the degradation potential of a recalcitrant dye, Acid blue 113, by hydrogen peroxide, ozone, hydroxyl radical and sulfate radical. Geometry optimization and frequency calculations were performed at ‘Hartree Fock’, ‘Becke, 3-parameter, Lee–Yang–Parr’ and ‘Modified Perdew-Wang exchange combined with PW91 correlation’ levels of study using 6-31G* and 6-31G** basis sets. The Fourier Transform-Raman spectra of Acid blue 113 were recorded and a complete analysis on vibrational assignment and fundamental modes of model compound was performed. Natural bond orbital analysis revealed that Acid blue 113 has a highly stable structure due to strong intermolecular and intra-molecular interactions. Mulliken charge distribution and molecular electrostatic potential map of the dye also showed a strong influence of functional groups on the neighboring atoms. Subsequently, the reactivity of the dye towards the oxidants was compared based on the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy values. The results showed that Acid blue 113 with a HOMO value -5.227 eV exhibits a nucleophilic characteristic, with a high propensity to be degraded by ozone and hydroxyl radical due to their lower HOMO-LUMO energy gaps of 4.99 and 4.22 eV respectively. On the other hand, sulfate radical and hydrogen peroxide exhibit higher HOMO-LUMO energy gaps of 7.92 eV and 8.10 eV respectively, indicating their lower reactivity towards Acid blue 113. We conclude that oxidation processes based on hydroxyl radical and ozone would offer a more viable option for the degradation of Acid blue 113. This study shows that quantum chemical analysis can assist in selecting appropriate advanced oxidation processes for the treatment of textile effluent.

Predicting absorption spectra of silver‐ligand complexes

AbstractThe detailed structures of most of ligand‐stabilized metal nanoclusters (NCs) remain unknown due to the absence of crystal structure data for them. In such a situation, quantum‐chemical modeling is of particular interest. We compared the performance of different theoretical methods of geometry optimization and absorption spectra calculation for silver‐thiolate complexes. We showed that the absorption spectra calculated with the ADC(2) method were consistent with the spectra obtained with CC2 method. Three DFT functionals (B3LYP, CAM‐B3LYP, and M06‐2X) failed to reproduce the CC2 absorption spectra of the silver‐thiolate complexes.

Study of 2,4-D Spectral Characteristics and Its Detection in Zizania Latifolia Using Terahertz Time-Domain Spectroscopy

2,4-Dichlorophenoxyacetic acid (2,4-D) is a common plant growth regulator, which can remain in food and, with long-term consumption, threaten human health. Therefore, it is necessary to propose an effective detection method. Terahertz time-domain spectroscopy technique (THz-TDS) has good advantages in the quantitative and qualitative analysis of most biomolecules due to its rich fingerprint characteristics. In this paper, density functional theory (DFT) was applied to geometry optimization and frequency vibration calculation of 2,4-D, and THz-TDS was used to quantitatively detect 2,4-D in Zizania latifolia. The results showed that there were three characteristic absorption peaks of 2,4-D at 1.36, 1.60, and 2.38 THz, respectively, and the theoretical spectra were in good consistency with experimental spectra, with slight discrepancies. Additionally, the absorption peak at 1.36 THz had the best absorption characteristics and was chosen as the main peak for 2,4-D quantitative analysis. It was demonstrated that the limits of detection (LOD) of 2,4-D in Zizania latifolia were found to be as low as 5%, the absorbance intensity at 1.36 THz showed a good linear relationship (R2 = 0.9854) with 2,4-D concentration from 5% to 30%, and the recovery was 93.29%–98.75%. Overall, this work enriched the fingerprint database of pesticide molecules on the basis of terahertz spectroscopy and could provide a technical support for the detection of 2,4-D in food by terahertz spectroscopy.

Effect of Fe Doping and O Vacancies on the Magnetic Properties of Rutile TiO2

Magnetism sources of Fe doping and O vacancies, which coexist in the presence of rutile TiO2, are controversial and require a resolution. The effects of Fe doping and point defect on the magnetism of rutile TiO2 were studied using geometry optimization and energy calculation based on the first principle generalized gradient approximation + U method (GGA+U) of density functional theory. Fe/Vo ratio is 1:1 in rutile TiO2. The next closest distance between Fe and Vo is 0.04082 nm. The formation energy of the doping system is the smallest. This doping system has the highest stability. The coexistence of Fe doping and O vacancy achieved ferromagnetic long-range order. The different ratios of Fe/Vo are 1:1, 1:2, 2:1, and 2:2. The magnetic properties of the doping system are significantly different. At a ratio of 2:1, the magnetic moment is the largest among all doping systems. Moreover, the Curie temperature of the doping system can be higher than room temperature. These findings can obtain dilute magnetic semiconductors with potential application value. At a Fe/VO ratio of 2:2, the Ti14Fe2O30 system produces a half-metallic property of 100% electron spin polarizability. This is the most valuable application for designing and preparing novel spintronic injection source dilute magnetic semiconductors. The magnetic source is mainly mediated by the holes generated by Fe doping and O vacancy complexes, thereby causing the spin polarization double exchange effect on the electron of Ti–3d orbital atoms near the O vacancy, O–2p electron orbital, and Fe–3d electron orbital. This feature is consistent with the following theories: the mean field approximation and the double exchange mechanism theories.

A theoretical study of regio and stereoselectivity nitration of thymol and carvacrol using DFT approach

This work is a detailed theoretical study of the nitration aromatic substitution reactions of thymol and carvacrol. In this process, a mixture of nitric and sulfuric acids is used to produce the nitronium agent NO 2 + . The computational calculations were performed at the Gaussian 09 using the DFT approaches. The first task of the computing study was to determine the optimized geometry of these compounds using the Becke three-parameter hybrid exchange functional and the Lee-Yang-Parr correlation functional (B3LYP) with the 6-311+G (d, p) basis set. Geometry optimization calculations have been carried out to find the global and local minima for reactants and intermediates, respectively, and to locate the saddle points for the transition states. The vibration frequencies have been calculated in order to check the character of the stationary points obtained after the geometry optimization. It is expected only positive frequencies for reactants, intermediates and products, but only one negative imaginary frequency for transition states. The analysis of the nucleophilic f k - Fukui Function and P k - Parr functions allows characterising the C 4 carbon atom as the most nucleophilic center of thymol and carvacrol, in clear agreement with the regioselectivity obtained. Calculation of activation energies, analysis of the potential energy surface and the Gibbs free energy indicates that this reaction takes place through a two-step mechanism.

Suspended CNT-Based FET sensor for ultrasensitive and label-free detection of DNA hybridization

A suspended carbon nanotube (SCNT)-based field effective transistor (SCNT-FET), which was fabricated by utilizing the surface tension of liquid silver to suspend a CNT between two Pd electrodes, was proposed for the detection of DNA hybridization. Benefits from the separation between the CNT and the substrates could be observed; namely, the conductivity of a SCNT-FET was much higher (two orders of magnitude) than that of a FET based on an unsuspended CNT and about 50% sensing surface of CNT was freed from substrate. The Slater-Koster tight-binding method was adopted for geometry optimization and transport property calculation of the SCNT bound with DNA. The result showed that the conductance (G = 1/R) of the SCNT decreased in order with the binding of single-stranded DNA (SSDNA, probe DNA) and double-stranded DNA (DSDNA) and that the ability of DSDNA to weaken the conductivity of the SCNT was several times higher than that of SSDNA. SEM and Raman spectroscopy were used to demonstrate that DNA could be bound successfully onto the SCNT using a 1-pyrenebutanoic acid succinimidyl ester (PBASE) as a linkage. Ultra-high sensitivity detection of DNA [with a limit of detection (LOD) as low as 10 aM] was obtained using such an SCNT-FET, which showed a lower value than that of a previously reported FET DNA biosensor whose sensing materials were in direct contact with the substrate.