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comparison of compound methods

Geometrical parametres formamidilnogo radical HNC (O) H (Tables 4.3, 4.4) are received with use [226]. It has been above shown, that in calculations for the same basis, but with various methods, the equilibrium structure formamidilnogo rayodikala can differ considerably, up to transferring to other point group simyometrii.

So table 4.3 contains the parametres which are falling into to nonplanar structure HNCOH, and Table 4.4 - to flat. Thus, equilibrium geometry in calculation «meyo
tod_1/bazis_1 », can not coincide essentially with that for"metod_2/bazis_2"if«метод_1»falls into to Table 4.3, and«метод_2»it is taken from Table 4.4. I.e. the condition blizoyosti geometry is not observed. Moreover, the analysis shows, that the geometry forms - dilnogo a radical from Table 4.4 is a transient state (TS) between two nonplanar conformstions (optical isomerides) found by means of methods of Table 4.3. ^edovatelno, Etotaιформамидильного a radical, defined by means of« metod_2/bazis_2//metod_1/bazis_1 », in any combination« metod_2/.//metod_1/. », if methods undertake from different tables, corresponds not to an equilibrium state, and TS. Cushche - stvujut and other connections (for example, CH3NO2 [303]) for which equilibrium geometyorija in"metod_1/bazis_1"that is not in"metod_2/bazis_2".

Tables 4.3 and 4.4 contain all steps by definition Etotaιиз G-w, CBS-w. If to analyse all sequence of procedures of any of specified difficult soyostavnyh methods [281, 299] it will appear, that the equilibrium geometry formamidilnogo a radical is in G-wi CbS-ws the help "metoda_1/bazisa_1" from Table 4.3, and Etota ι (and Htota ι) - "metodom_2/bazisom_2" from Table 4.4. ^edovatelno, difficult compound meyotody yield Etotaιи Htotalформамидильного a radical for essentially nonequilibrium geoyometrii (close to TS) and cannot be used at definition of standard enthalpy of formation HNC (O) H. At the same time, it is necessary to notice, that compound methods (as spoyosob definitions Etota ι) are applicable in all cases, but EtotaI, probably, will concern not a minimum on Ш1Э, and to any other point.

Use as simple («metod_2/bazis_2//metod_1/bazis_1»), and difficult (G-w, CBS-w, W-w) compound methods bears in itself a certain share of luck. If geoyometrija, optimised at the first stage, remains equilibrium for the subsequent etayopov use of these methods is justified. If the yielded condition is not carried out, application of compound methods for definition of thermodynamic properties in dalnejyoshem will inevitably lead to incorrect result. 1ри it, the total error ∆y H0будет, first of all, to be defined by a deviation of geometry from equilibrium on each of steps. For example, application of difficult compound methods or a certain configuration simple («метод_1» from Table 4.3, «метод_2» from Table 4.4 and, naoboyorot) for formamidilnogo a radical is incorrect.

Probably with it, in opredeyolennoj to a measure, known difficulties of difficult compound methods, partially reyoshaemye by introduction «vysokourovnevyh empirical corrections» [300-302] are connected.

Thermodynamic and thermochemical properties of molecules and radicals in sootvetyostvujushchih databases are classified as: "recommended" ("tabulated"), "pre-award", "doubtful" and "unacceptable" (see, for example, [127]). C this
The points of view ΔfH0и other properties HNC (O) H, found by means of G-n, CBS-n, W - n, fall into "unacceptable", and the properties of other substances found without any comparisons, it is necessary to classify as "doubtful" or, at the best, "pre-award". The considered example shows, that use of compound methods demands special attention when on each step of calculation, and not just at a stage of optimisation of geometry, convergence conditions should be resulted. Those are differences energy and standard deviations of factors of a matrix of density in last cycle of iterative procedure. Besides it is necessary to result and proveyorjat values of forces (gradients), and, on-possibility, vibration frequencies. Discrepancy of the specified sizes (the big gradients, imaginary frequencies) is powerful argument for refusal of corresponding value of energy. Modern computer programyomy give out the specified sizes on each step (except for a spectrum), and prevysheyonie certain borders will speak about inapplicability of compound methods in rasyosmatrivaemom a case. Full of energy of reference-point substances are shown in Tables 4.5 - 4.9.

Table 4.6. Full energy-Etota ι//-alkanes and/-alkilnyh the radicals, calculated metoyodom B3LYP/6-311 ++ G (3df, 3pd) in program GAUSSIAN, in a.e.

Molecule AND, G AND, IN Δ, a kdzh/MOLE Radical AND, G AND, IN Δ, a kdzh/MOLE
С2Н6 79,862776 79,864128 -3,5 CH3CH∙2 79,191139 79,192494 -3,6
C3H8 119,190195 119,192292 -5,5 CILCH-CIU 118,518302 118,520397 -5,5
С4Н10 158,517448 158,520277 -7,4 CH3 (CH2) 2CH∙2 157,845598 157,848423 -7,4
С5Н12 197,844621 197,848177 -9,3 CH3 (CH2) 3CH∙2 197,172781 197,176333 -9,3
C6 ‰ 237,171797 237,176088 -11,3 CH3 (CH2) 4CH∙2 236,499962 236,504242 -11,2
С7Н16 276,498972 276,503992 -13,2 CH3 (CH2) 5CH∙2 275,827138 275,832152 -13,2
С8Н18 315,826125 315,831871 -15,1 CH3 (CH2) 6CH∙2 315.154269 315,160012 -15,1
С9Н20 355.153248 355.159798 -17,2 CH3 (CH2) 7CH∙2 354.487919 -
С10Н22 394.480412 394.487700 -19,1 CH3 (CH2) 8CH∙2 393.808590 393,815863 -19,1

In - the Cartesian functions (6d 10f), G - spherical harmonics (5d 7f)

Δ - a difference full energy, found by means of B3LYP/6-311 ++ G (3df, 3pd) 6d

10f and B3LYP/6-311 ++ G (3df, 3pd) 5d 7f

Table 4.7. Full energy Etota ι///-nitroalkanes and/-nitroalkilnyh radicals, rasschi -

tannaja a method. 33LYP/6-311 ++ G (3df, 3pd) in various bases, in a.e.
Molecule AND, G

GAUSSIAN

A IN GAUSSIAN Radical G

GAUSSIAN

CH3NO2 -245.109670 -245.115019 CH7NO7 -244.462639987
C2H5NO2 -284.440728 -284.446685 C2H4NO2 -283.794201717
C3H7NO2 -323.768111 -323.774912 C3⅛NO2 -323.126162972
C4H9NO2 -363.095468 -363.103007 C4H8NO2 -362.457330055
C5H11NO2 -402.422747 -402.431006 C5H10NO2 -401.788722687
(HNLL -441.749994 -441.758987 C6H12NO2 -441.119782583
C7Hl5NO2 -481.077194 -481.086922 C7H14NO2 -480.450804709
C8H17NO2 -520.404387 -520.414785 C8H16NO2 -
C9H19NO2 -559.731572 -559.742689 C9H18NO2 -
C10H21NO2 -599.058752 -599.070669 - -

And - basis 6-311 ++ G (3df, 3pd), - basis aug-cc-pVQZ

In - the Cartesian functions (6d 10f), G - spherical harmonics (5d 7f) * 5d 7f

** GAUSSIAN b3lyp∕aug-cc-pv5z 5d 7f

сGAUSSIAN b3lyp∕cc-pvQZ 6d 10f

Table 4.8. Full energy of formamide-Etota ι, in a.e. (1 a.e. = 2625,4997 kdzh/MOLE). For compound methods the empirical correction »HLC (⅞⅛ piric) ∙ is specified« vysokourovnevaja

Method Etotal EEmpiric EEmpiric

*

Method Etotal EEmpiric EEmpiric

*

Method Etotal
G1 169,686273 0,055260 145,09 CBS -

4M

169,722779 0,116078 304,76 B3LYP∕6 -

311 ++ G (3df, 3pd)

5d 7f

169,967074
G2 169,686273 0,055260 145,09 CBS -

4O

169,720680 0,113450 297,86 B3LYP∕6 -

311 ++ G (3df, 3pd)

6d 10f

169.970400
G2 MP2 169,684916 0,045000 118,15 CBS -

Lq

169,745365 0,106490 279,59 B3LYPAUG-CC - pV5Z 5d 7f 169,986327
G3 169,828853 0,057474 150,90 CBS-Q 169,697047 0,026694 70,09 MP2 (full) ∕6 -

311 ++ G (3df, 3pd)

169,679715
G3B3 169,832326 0,060840 159,74 CBS -

QB3

169,698421 0,029031 76,22 MP2∕aug-cc-pV 5Z 169,686688
G3 MP2 169,711304 0,083511 219,26 CBS - APNO 169,893440 0,008187 21,49 MP4SDTQ∕6 - 311 ++ G (3df, 3pd) 169,652496
G3 MP2B3 169,718248 0,090369 237,26 W1 170,025359 0,00 0,00 - -

*в a kdzh/MOLE

Table 4.9. Full energy formamidilnogo a radical-Etota ι, in a.e.

HFAUG-CC - pV5Z MP2AUG - cc-pVQZ MP4SDTQ ∕

6-311G (d, p)

B3LYP ∕ AUG-CC - pV5Z CCSD (T) 6-311 ++ G (3df, 3p d) QCISD∕6 - 311 ++ G (3df, 3pd) CISD∕6 -

311 ++ G (3df

, 3pd)

CID∕6 -

311 ++ G (3d

f, 3pd)

168.372422 168,968402 168,844355 169.294053 168.956125 168.934057 168.867788 168.864761

4.3.

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A source: Turovtsev Vladimir Vladimirovich. Creation and application of a quantum mechanical model for calculating the thermodynamic properties of substances in a wide range of temperatures. Thesis for the degree of doctor of physico-mathematical sciences. Tver - 2014. 2014

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