Quadruple-zeta Basis Set Research Articles

Ab initio spectroscopic studies of AlF and AlCl molecules

In this work, we report the results from our spectroscopic study on AlF and AlCl molecules. We carry out detailed electronic structure calculations in both the molecules, including obtaining the potential energy surfaces of the [Formula: see text] ground electronic state and some of the low-lying excited electronic states belonging to [Formula: see text] and [Formula: see text] symmetries. This is followed by evaluating the spectroscopic constants and molecular properties such as electric dipole moments and electric quadrupole moments. Throughout, we employ the multi-reference configuration interaction method and work with high-quality quadruple zeta basis sets. Further, transition dipole moments between the ground electronic state and singlet excited states are also studied. The relevant vibrational parameters are computed by solving the vibrational Schrödinger equation. Subsequently, the vibrational energy spacings and transition dipole moments between the vibrational levels belonging to the same electronic states are used to evaluate the spontaneous and black-body radiation-induced transition rates, followed by computing the lifetimes. Finally, the energy differences between rotational levels belonging to different vibrational levels and within an electronic state as well as the Einstein coefficients are reported.

Isomerism of : Accurate structural, energetic, and spectroscopic characterization.

A recent work [Ye et al. Mon. Not. R. Astron. Soc. 2023, 525, 1158] on the gas-phase formation of t-HC(O)SH, already detected in the interstellar medium, pointed out that the trans form of HC(S)OH is a potential candidate for astronomical observations. Prompted by these results, the family of isomers has been investigated from an energetic point of view using a double-hybrid density functional in combination with a partially augmented triple-zeta basis set. This preliminary study showed that the most stable species of the family are the cis and trans forms of HC(O)SH and HC(S)OH. For their structural and spectroscopic characterization, a composite scheme based on coupled cluster (CC) calculations that incorporates up to the quadruple excitations and accounts for the extrapolation to the complete basis set limit and core correlation effects has been employed. This approach opens to the prediction of rotational constants with an accuracy of 0.1%. A hybrid scheme, based on harmonic frequencies computed using the CC singles, doubles and a perturbative treatment of triples method (CCSD(T)) in conjunction with a quadruple-zeta basis set, allowed us to obtain fundamental vibrational frequencies with a mean absolute error of about 1%.

High-accuracy DMBE potential energy surface for CNO(A''4) and the rate coefficients for the C + NO reaction in the A'2, A''2, and A''4 states.

An accurate potential energy surface (PES) for the lowest lying A''4 state of the CNO system is presented based on explicitly correlated multi-reference configuration interaction calculations with quadruple zeta basis set (MRCI-F12/cc-pVQZ-F12). The abinitio energies are fitted using the double many-body expansion method, thus incorporating long-range energy terms that can accurately describe the electrostatic and dispersion interactions with physically motivated decaying functions. Together with the previously fitted lowest A'2 and A''2 states using the same theoretical framework, this constitutes a new set of PESs that are suitable to predict rate coefficients for all atom-diatom reactions of the CNO system. We use this set of PESs to calculate thermal rate coefficients for the C(P3) + NO(Π2) reaction and compare the temperature dependence and product branching ratios with experimental results. The comparison between theory and experiment is shown to be improved over previous theoretical studies. We highlight the importance of the long-range interactions for low-temperature rate coefficients.

Quantifying Intramolecular Basis Set Superposition Errors.

We show that medium-sized Gaussian basis sets lead to significant intramolecular basis set superposition errors at Hartree-Fock and density functional levels of theory, with artificial stabilization of compact over extended conformations for a 186 atom deca-peptide. Errors of ∼80 and ∼10 kJ/mol are observed, with polarized double zeta and polarized triple zeta quality basis sets, respectively. Two different procedures for taking the basis set superposition error into account are tested. While both reduce the error, it appears that polarized quadruple zeta basis sets are required to reduce the error below a few kJ/mol. Alternatively, the basis set superposition error can be eliminated using multiresolution methods based on Multiwavelets.

Relativistic calculations of molecular electric dipole moments of singly charged aluminium monohalides

In this work, we have studied the permanent electric dipole moments of singly charged aluminum monohalides in their electronic ground state, , using Kramers-restricted relativistic configuration interaction method. We report our results from this method in the singles and doubles approximation with those of Dirac–Fock calculations. For our finite field computations, quadruple zeta basis sets were employed. We discuss the electron correlation trends that we find in our calculated properties and have compared our results with those from literature, wherever available.

Complexes of LiF and LiCl with LiF, LiCl, LiH, HF, HCl, H2, Li2, F2, Cl2, FCl, H2O and NH3. Structures, energies and vibrational frequencies

Using coupled cluster calculations with quadruple-zeta basis sets optimal structures and dissociation energies were obtained for complexes of LiF and LiCl with LiH, HF, HCl, H2, Li2, F2, Cl2, FCl, H2O and NH3. Structures for LiF-LiF and LiCl-LiCl have D2h symmetry, while the structure of LiF-LiCl, as well as structures of LiF and LiCl with LiH, HF and Li2 are cyclic, with C2v symmetry. Most other systems have Cs symmetry, many in near-cyclic form. The largest dissociation energy of 21,304 cm−1 was obtained for LiF-LiF. Dissociation energies for LiCl-LiCl and for cyclic C2v systems range from about 10,000 to 20,000 cm−1. For cyclic systems with D2h and C2v symmetries harmonic vibrational frequencies cannot be related to monomer frequencies. Their higher frequencies, however, are close to frequencies of triatomic Li-Y-Li, with Y = H, F, Cl, and to frequencies of F-H-F-.

ωB97X-3c: A composite range-separated hybrid DFT method with a molecule-optimized polarized valence double-ζ basis set.

A new composite density functional theory (DFT) method is presented. It is based on ωB97X-V as one of the best-performing density functionals for the GMTKN55 thermochemistry database and completes the family of "3c" methods toward range-separated hybrid DFT. This method is consistently available for all elements up to Rn (Z = 1-86). Its further key ingredients are a polarized valence double-ζ (vDZP) Gaussian basis set, which was fully optimized in molecular DFT calculations, in combination with large-core effective core potentials and a specially adapted D4 dispersion correction. Unlike most existing double-ζ atomic orbital sets, vDZP shows only small basis set superposition errors (BSSEs) and can compete with standard sets of triple-ζ quality. Small residual BSSE effects are efficiently absorbed by the D4 damping scheme, which overall eliminates the need for an explicit treatment or empirical corrections for BSSE. Thorough tests on a variety of thermochemistry benchmark sets show that the new composite method, dubbed ωB97X-3c, is on par with or even outperforms standard hybrid DFT methods in a quadruple-zeta basis set at a small fraction of the computational cost. Particular strengths of this method are the description of non-covalent interactions and barrier heights, for which it is among the best-performing density functionals overall.

Ipie: A Python-Based Auxiliary-Field Quantum Monte Carlo Program with Flexibility and Efficiency on CPUs and GPUs.

We report the development of a python-based auxiliary-field quantum Monte Carlo (AFQMC) program, ipie, with preliminary timing benchmarks and new AFQMC results on the isomerization of [Cu2O2]2+. We demonstrate how implementations for both central and graphical processing units (CPUs and GPUs) are achieved in ipie. We show an interface of ipie with PySCF as well as a straightforward template for adding new estimators to ipie. Our timing benchmarks against other C++ codes, QMCPACK and Dice, suggest that ipie is faster or similarly performing for all chemical systems considered on both CPUs and GPUs. Our results on [Cu2O2]2+ using selected configuration interaction trials show that it is possible to converge the ph-AFQMC isomerization energy between bis(μ-oxo) and μ-η2:η2 peroxo configurations to the exact known results for small basis sets with 105-106 determinants. We also report the isomerization energy with a quadruple-zeta basis set with an estimated error less than a kcal/mol, which involved 52 electrons and 290 orbitals with 106 determinants in the trial wave function. These results highlight the utility of ph-AFQMC and ipie for systems with modest strong correlation and large-scale dynamic correlation.

Copper-Catalyzed Aromatic Fluorination of 2-(2-bromophenyl)pyridine via Cu(I)/Cu(III) Mechanism in Acetonitrile Solvent: Cluster-Continuum Free Energy Profile and Microkinetic Analysis

Nucleophilic fluorination via copper catalysis has been a challenging transformation and only special substrates can react. One example is the 2-(2-bromophenyl)pyridine, which was fluorinated with AgF using CuPF6 catalyst in acetonitrile solvent. In this work, a detailed analysis of this catalyzed reaction was done using theoretical methods. The free Cu+ ion and the CuF ion pair in acetonitrile solvent were modeled using a quasi-chemical cluster-continuum approach and electronic energies calculated at DLPNO-CCSD(T) level with a quadruple-zeta basis set. The catalytic cycle involves the Cu(I)/Cu(III) mechanism via cationic (Cu+ ion) or neutral (CuF ion pair) pathways. The solubility of AgF and CuF was included in the analysis, as well as the transmetalation step. The calculated free energy profile was used to perform a microkinetic analysis of the reaction system. The results point out that the reaction proceeds via the cationic mechanism, with the formation of the catalyst-substrate complex followed by the oxidative addition step with ΔG‡ = 30.8 kcal mol−1. The formed intermediate is high in free energy and the reductive elimination step is the rate-determining one, with an overall ΔG‡ = 32.6 kcal mol−1. Analysis of the free energy profile and the microkinetic modeling point out almost zero-order kinetics in substrate concentration when the catalyst is used in substoichiometric quantity. Approximated experimental ΔG‡ is estimated as being 30.7 kcal mol−1, in very good agreement with the theoretical value. The neutral mechanism with the soluble CuF ion pair has ΔG‡ = 33.4 kcal mol−1, which is competitive with the cationic mechanism. However, due to the low solubility and concentration of this ion pair, the reaction does not take place by this pathway.

A Full-Dimensional ab initio Intermolecular Potential Energy Surface and Dipole Moment Surfaces for H2O-Ar

Background: The H2O–Ar system has attracted significant interest in recent years because it is an important model to study inelastic scattering between atoms and triatomic molecules. A high-accuracy intermolecular potential energy surface (IPES) is the foundation for theoretical study on molecular collision dynamics for H2O–Ar. In addition, dipole moment surfaces (DMSs) are one of the prerequisites for spectral simulation. Objective: This study aimed to obtain a full-dimensional intermolecular potential energy surface and dipole moment surfaces for the van der Waals complex H2O–Ar. Methods: In this study, ab initio energy points were computed at the frozen-core (FC) explicitly correlated coupled-cluster [FC-CCSD(T)-F12a] level, with the augmented correlation-consistent polarized valence quadruple-zeta basis set plus bond functions. The permutation invariant polynomial neural network (PIP-NN) approach is adopted to fit the IPES, while the DMSs are constructed at the MP2/AVTZ level and fitted by the NN approach. Results: With a root-mean-square-error (RMSE) of 0.284 cm-1, the IPES can accurately describe the motion of the H2O–Ar complex between R = 4 and 20 a0 in the energy range up to 10000 cm-1. The fitting errors of all the data points are 6.192 and 6.509 mDebye for the X and Z components, respectively. The global minimum of -140.633 cm-1 has the plane geometry, while the dipole moment of H2O–Ar is 1.853 Debye at the equilibrium structure. Conclusion: In summary, we report a full-dimensional intermolecular potential energy surface for H2O–Ar. The IPES precisely reproduces CCSD(T)-F12a electronic energies with a large basis set. The corresponding dipole moment surfaces have also been reported. In comparison with previous work, the employment of the high-level ab initio method will make our IPES more reliable. Several typical 2D contour plots of the IPES and DMSs are also shown. The argon atom has a weak effect on the dipole moment of the H2O–Ar complex. The FORTRAN codes to generate 6D potentials and dipole moments reported here are available on request from the authors.

Performance of a one-parameter correlation factor for transcorrelation: Study on a series of second row atomic and molecular systems.

In this work, we investigate the performance of a recently proposed transcorrelated (TC) approach based on a single-parameter correlation factor [E. Giner, J. Chem. Phys. 154, 084119 (2021)] for systems involving more than two electrons. The benefit of such an approach relies on its simplicity as efficient numerical-analytical schemes can be set up to compute the two- and three-body integrals occurring in the effective TC Hamiltonian. To obtain accurate ground state energies within a given basis set, the present TC scheme is coupled to the recently proposed TC-full configuration interaction quantum Monte Carlo method [Cohen et al., J. Chem. Phys. 151, 061101 (2019)]. We report ground state total energies on the Li-Ne series, together with their first cations, computed with increasingly large basis sets and compare to more elaborate correlation factors involving electron-electron-nucleus coordinates. Numerical results on the Li-Ne ionization potentials show that the use of the single-parameter correlation factor brings on average only a slightly lower accuracy (1.2 mH) in a triple-zeta quality basis set with respect to a more sophisticated correlation factor. However, already using a quadruple-zeta quality basis set yields results within chemical accuracy to complete basis set limit results when using this novel single-parameter correlation factor. Calculations on the H2O, CH2, and FH molecules show that a similar precision can be obtained within a triple-zeta quality basis set for the atomization energies of molecular systems.

Copper-mediated aromatic fluorination using N-heterocycle-carbene ligand: Free energy profile of the Cu(I)/Cu(III) and Cu(II) radical mechanisms

Addition of fluorine to organic molecules in the late stage of synthesis has been an increased interest in the past decade. Catalytic methods using fluoride salts as reagents could be especially useful, mainly with the use of organometallic catalysis with copper. Recent experimental advances have been reported for copper-mediated fluorination and the development of an efficient catalytic process needs a deep understanding of the reaction mechanism and the free energy profile. In this work, different mechanisms of copper-mediated fluorination of 2-(2-bromophenyl)pyridine using LCuF as reagent (L = N-heterocycle-carbene ligand) were investigated using very high level of theory, DLPNO-CCSD(T) method with up to quadruple-zeta basis set. The Cu(I)/Cu(III) mechanism is the predominant one, taking place via neutral (MS2) or cationic (MS2p) intermediates. Although the oxidative addition step has high barrier, the reductive elimination was found to be the rate-determining step. Three reaction pathways involving the Cu(II) radical mechanism was also investigated. The first one is the single-electron transfer mechanism and the second is the bromine atom transfer in the first step. Both pathways involve high free energy intermediates and are inviable. The third mechanism occurs via singlet-triplet spin crossover with bromine transfer from the oxidative addition intermediate MS2 to the LCuF initial reagent. However, the reductive elimination step from the MS2r doublet Cu(II) complex is much more difficult than the MS2 or MS2p singlets of Cu(III) complexes, leading to a very slow kinetics for this Cu(II) radical mechanism. The kinetics analysis of the theoretical free energy profile results in effective ΔG‡ of 30.6 kcal mol−1, in good agreement with an estimated experimental value and providing an important support for the Cu(I)/Cu(III) mechanism.

Concerted addition of aldehydes to the singlet biradical [P(μ-NTer)]2.

The reaction of the singlet biradical [P(μ-NTer)]2 with various aldehydes selectively yielded the corresponding [2.1.1]-bicyclic addition products in a very fast reaction. All products were fully characterized, including by NMR and vibrational spectroscopy as well as single-crystal X-ray diffraction. The mechanism of the addition was investigated theoretically using high-level ab initio methods (CCSD(T) with triple- and quadruple-zeta basis sets) and corresponds to a concerted cycloaddition reaction with a very low activation barrier. For comparison, the mechanisms of the literature-known cycloadditions of H2, alkenes, and alkynes were also studied, indicating a similar reaction profile for all unsaturated reactants.

Deexcitation rate coefficients of C3 by collision with H2 at low temperatures

Context. An accurate analysis of the physical-chemical conditions in the regions of the interstellar medium in which C3 is observed requires knowing the collisional rate coefficients of this molecule with He, H2, electrons, and H. Aims. The main goals of this study are to present the first potential energy surface for the C3 +H2 complex, to study the dynamics of the system, and to report a set of rate coefficients at low temperature for the lower rotational states of C3 with para- and ortho-H2. Methods. A large grid of ab initio energies was computed at the explicitly correlated coupled-cluster with single-, double-, and perturbative triple-excitation level of theory, together with the augmented correlation-consistent quadruple zeta basis set (CCSD(T)-F12a/aug-cc-pVQZ). This grid of energies was fit to an analytical function. The potential energy surface was employed in close-coupling calculations at low collisional energies. Results. We present a high-level four-dimensional potential energy surface (PES) for studying the collision of C3 with H2. The global minimum of the surface is found in the linear HH-CCC configuration. Rotational deexcitation state-to-state cross sections of C3 by collision with para- and ortho-H2 are computed. Furthermore, a reduced two-dimensional surface is developed by averaging the surface over the orientation of H2. The cross sections for the collision with para-H2 using this approximation and those from the four-dimensional PES agree excellently. Finally, a set of rotational rate coefficients for the collision of C3 with para- and ortho-H2 at low temperatures are reported.

Chemical accuracy with σ-functionals for the Kohn-Sham correlation energy optimized for different input orbitals and eigenvalues.

Recently, a new type of orbital-dependent functional for the Kohn-Sham (KS) correlation energy, σ-functionals, was introduced. Technically, σ-functionals are closely related to the well-known direct random phase approximation (dRPA). Within the dRPA, a function of the eigenvalues σ of the frequency-dependent KS response function is integrated over purely imaginary frequencies. In σ-functionals, this function is replaced by one that is optimized with respect to reference sets of atomization, reaction, transition state, and non-covalent interaction energies. The previously introduced σ-functional uses input orbitals and eigenvalues from KS calculations with the generalized gradient approximation (GGA) exchange-correlation functional of Perdew, Burke, and Ernzerhof (PBE). Here, σ-functionals using input orbitals and eigenvalues from the meta-GGA TPSS and the hybrid-functionals PBE0 and B3LYP are presented and tested. The number of reference sets taken into account in the optimization of the σ-functionals is larger than in the first PBE based σ-functional and includes sets with 3d-transition metal compounds. Therefore, also a reparameterized PBE based σ-functional is introduced. The σ-functionals based on PBE0 and B3LYP orbitals and eigenvalues reach chemical accuracy for main group chemistry. For the 10966 reactions from the highly accurate W4-11RE reference set, the B3LYP based σ-functional exhibits a mean average deviation of 1.03 kcal/molcompared to 1.08 kcal/molfor the coupled cluster singles doubles perturbative triples method if the same valence quadruple zeta basis set is used. For 3d-transition metal chemistry, accuracies of about 2 kcal/molare reached. The computational effort for the post-self-consistent evaluation of the σ-functional is lower than that of a preceding PBE0 or B3LYP calculation for typical systems.

Efficient Ab Initio Estimation of Formation Enthalpies for Organic Compounds: Extension to Sulfur and Critical Evaluation of Experimental Data.

The efficient protocol for the estimation of gas-phase enthalpies of formation developed previously for C, H, O, N, and F elements was extended to sulfur. The protocol is based on a local coupled cluster with single, double, and perturbative triple excitation [CCSD(T)] approximation and allows rapid evaluation of compounds with sizes computationally prohibitive to canonical CCSD(T) using quadruple zeta basis sets. As a part of model development, a comprehensive review and critical evaluation of experimental data were performed for 87 sulfur-containing organic and inorganic compounds. A compact model with only three empirical parameters for sulfur introduced to address the effects beyond frozen core CCSD(T) was developed. The model exhibits approximately 2 kJ·mol-1 standard deviation over a set of experimental values for a diverse collection of sulfur-containing compounds. The complete basis set version of the model demonstrates a similar performance and requires only one empirical parameter. Multiple problems with the existing experimental data were identified and discussed. In addition, a lack of reliable data for certain important classes of sulfur compounds was found to impede the model generalization and confident performance assessment.

A full-dimensional ab initio intermolecular potential energy surface and rovibrational spectra for OC-HF and OC-DF.

We present a full-dimensional ab initio intermolecular potential energy surface (IPES) for the OC-HF van der Waals complex. 3167 ab initio points were computed at the frozen-core (FC) explicitly correlated coupled cluster [FC-CCSD(T)-F12b] level, with the augmented correlation-consistent polarized valence quadruple-zeta basis set plus bond functions. Basis set superposition error correction was also considered by the full counterpoise procedure. Gaussian process regression (GPR) was used to map out the potential energy surface, while a multipole expansion method was employed to smooth the ab initio noise of intermolecular potential in the long range. The global minimum of -1248.364cm-1 was located at the linear configuration with the C atom pointing toward the H atom of the HF molecule. In addition, a local minimum of -602.026cm-1 was found at another linear configuration with the O atom pointing toward the H atom of the HF molecule. The eigenstates were calculated on the vibrational averaged four-dimensional IPESs with the mixed radial discrete variable representation/angular finite basis representation method and Lanczos propagation algorithm. The dissociation energy D0 was calculated to be 701.827cm-1, well reproducing the experimental value of 732 ± 2cm-1. The dipole moment surfaces were also fitted by GPR from 3132 ab initio points calculated using the coupled cluster method [CCSD(T)] with AVTZ basis set plus bond functions. The frequencies and relative line intensities of rovibrational transitions in the HF (DF) and CO stretching bands were further calculated and compared well with the experimental results. These results indicate the high fidelity of the new IPES.

TESTING OF THE OPTIMUM BASIS SET FOR MODELING THE HEXABROMOTELURATE ANION

Using the PRIRODA 19 program, the bond lengths Te–Br have been calculated for the hexabromotelurate anion [TeBr6]2– within the frameworks of the GGA PBE density functional theory and the Møller–Plesset second order perturbation theory. In order to find the optimum basis set, the λXa (where X = 1-4) basis sets developed by D. Laikov, with diffusion functions, were tested. It must be noticed that in the case of the λXa (where X = 1-4) basis sets, the anion [TeBr6]2– is described by different numbers of basis functions: 261 for the double-zeta basic set λ1a, 422 for the triple-zeta basic set λ2a, 660 and 989 for the basis sets λ3a and λ4a, respectively. As the system under investigation contains relatively heavy atoms, the relativistic effects were taken into account using the four-component scalar-relativistic Hamiltonian by Dirac and using the new two-component AAA Hamiltonian by Laikov.
 The optimization of the geometric parameters of the hexabromotelurate anion was carried out with no symmetry restrictions. In all cases, the optimized [TeBr6]2– geometry corresponds to the nearly perfect octahedral symmetry; so the average Te–Br bond lengths have been considered. In the case of the PBE/λXa method (where X = 1-4), an increase in the size of the basis set results in a shortening of the Te–Br bond lengths. It has been shown that the difference between the four-component and two-component relativistic approximations increases with an increase of the basic set used. In turn, in the case of the MP2 method, the difference between the four-component and two-component relativistic approximations decreases with an increase of the basic set, and goes through the minimum for the quadruple-zeta λ3a basis set. Thus, in the post-Hartree–Fock approach, such as the Møller–Plesset perturbation theory and the coupled clusters theory, the agreement between the above relativistic approximations is reasonably good, and the two-component scalar-relativistic AAA Hamiltonian by Laikov (which is characterized by much lesser recourse demands) is more optimal for a variety of «heavy» and time-consuming calculations at the higher levels of theory. For modeling the geometric parameters of hexabromotelurate anion with an accuracy of 0.01 Å, we recommend the use of the triple-zeta basis set with the scalar-relativistic Hamiltonian.

Infrared Spectrum for the New Nanomolecules ASi, CSi, TSi and Gsi

The core of the work is based on the replacement of carbon atoms by silicon atoms, on the basis of four standard bases of DNA: A, C, G and T (adenine, cytosine, guanine, thymine). Determining with minimum computational methods via ab initio Hartree-Fock methods, infrared spectrum and their peak absorbance frequencies. The option for simple replacement of carbon by silicon is due to the peculiar characteristics between both. Atomic interactions under non-carbon conditions were studied, with only the Hydrogen, Silicon, Nitrogen and Oxygen atoms, in CNTP, for the four standard bases of DNA, A, C, G and T, thus obtaining by quantum chemistry four new compounds, named here as: ASi, CSi, GSi and TSi. Computational calculations admit the possibility of the formation of such molecules, their existence being possible via quantum chemistry. Calculations obtained in the ab initio Unrestricted and Restrict Hartree-Fock method, (UHF and RHF) in the set of bases used Effective core potential (ECP) minimal basis, UHF CEP-31G (ECP split valance) and UHF CEP-121G (ECP triple-split basis), CC-pVTZ (Correlation-consistent valence-only basis sets triple-zeta) and 6-311G**(3df, 3pd) (Gaussian functions quadruple-zeta basis sets).

Infrared Spectrum for the New Exobiological Nanomolecules Asi, Csi, Tsi and Gsi

The core of the work is based on the replacement of carbon atoms by silicon atoms, on the basis of four standard bases of DNA: A, C, G and T (adenine, cytosine, guanine, thymine). Determining with minimum computational methods via ab initio Hartree-Fock methods, infrared spectrum and their peak absorbance frequencies. The option for simple replacement of carbon by silicon is due to the peculiar characteristics between both. Atomic interactions under non-carbon conditions were studied, with only the Hydrogen, Silicon, Nitrogen and Oxygen atoms, in CNTP, for the four standard bases of DNA, A, C, G and T, thus obtaining by quantum chemistry four new compounds, named here as: ASi, CSi, GSi and TSi. Computational calculations admit the possibility of the formation of such molecules, their existence being possible via quantum chemistry. Calculations obtained in the ab initio Unrestricted and Restrict Hartree-Fock method, (UHF and RHF) in the set of basis used Effective core potential (ECP) minimal basis, UHF CEP-31G (ECP split valance) and UHF CEP-121G (ECP triple-split basis), CC-pVTZ (Correlation-consistent valence-only basis sets triple-zeta) and 6-311G**(3df, 3pd) (Gaussian functions quadruple-zeta basis sets).