Presentation is loading. Please wait.

Presentation is loading. Please wait.

Dr. Ivan Rostov Australian National University, Canberra

Similar presentations


Presentation on theme: "Dr. Ivan Rostov Australian National University, Canberra"— Presentation transcript:

1 Dr. Ivan Rostov Australian National University, Canberra E-mail: Ivan.Rostov@anu.edu.au

2  Types of solvent effects and solvent models  Overview of solvation continuum models available in Gaussian 03.  Summary of Gaussian keywords  Applications  Recommendations 2

3 3 Nicolai Alexandrovich Menshutkin, Z. Physik. Chem. 1890, 5, 589 NH 3 CH 3 ClNH 3 CH 3 + Cl 

4  The solvent environment influences all of these: Structure Energies Reaction and activation energies Bond energies Spectra Rotational (Microwave) Vibrational (IR, Raman) Electronic (UV, visible) 4

5  Supermolecule  Solute and some number of solvent molecules are included in one large QM calculation  Molecular Mechanics Force Fields  Simple classical force fields allows us to include a large number of solvent molecules  Continuum models  Explicit consideration of solvent molecules is neglected  Solvent effects are described in terms of macroscopic properties of the chosen solvent ( , )  Hybrid/mixed:  Supermolecule + Continuum model  QM + MM  QM + MM + Continuum model 5

6 6 1) Creation of cavity 3) Turning on electrostatic forces 2) Turning on dispersion and repulsion forces

7  Solvent is described in terms of macroscopic properties  Solvent is dielectric medium (uniform, normally), characterized by the dielectric constant    Polarization of solvent is expressed in terms of the surface charge density on the cavity surface  Polarization produces the electric field in the cavity making an effect on solute  Dispersion-Repulsion and Cavitation are added separately, or ignored 7

8 8 Solution is calculated as Poisson equations with boundary conditions on S:

9 9  A single charge inside a spherical cavity  No constructing of the cavity surface elements, because the Poisson equation is solved analytically

10  Spherical cavity  Dipolar reaction field  No constructing of the cavity surface elements, because the Poisson equation is solved analytically  Keywords in Gaussian: SCRF(Dipole,A0=value,Dielectric=value)  Area of applicability:  Solute shape is close to spherical  Solute is polar (  >> 0)  References  L. Onsager, J. Am. Chem. Soc. 58, 1486 (1936).  M. Wong, M. Frisch, K. Wiberg, J. Am. Chem. Soc. 113, 4476 (1991). 10

11  Realistic molecular shape of the cavity (interlocking spheres around each atom or group, or isodensity surface)  Induced surface charges represent solvent polarization  Includes free energy contributions from forming the cavity and dispersion-repulsion  Comes in number of “flavours”: IEFPCM, CPCM, DPCM, IPCM, or SCIPCM  Keywords in Gaussian:  SCRF(Solvent=, PCM specific options)  References:  E. Canses, B. Mennucci, J. Tomasi, J. Chem Phys. 107, 3032 (1997).  J. Tomasi, M. Persico, Chem. Rev. 94,2027 (1994).  J. Tomasi, B. Mennucci, R. Camm, Chem. Rev. 105, 2999 (2005). 11

12  Interlocking spheres around atomic groups  This is default in Gaussian 03  A choice of united atoms radii set, RADII=UAO (default), UAHF, UAKS, or UFF  Interlocking spheres around each atom  Radii=Pauling (or Bondi)  Requires the scaling factor ALPHA by which the sphere radius is multiplied. The default value is 1.0 though should be 1.2  A number of keywords is provided to add extraspheres when necessary  A number of keyword is provided to govern the size and number of surface elements (tesserae) 12

13  Keyword: GeomView  Creates files in GeomView format to visualize the cavity construction and the charge distribution on the cavity:  tesserae.off  charge.off Files are readable by GeomView, JavaView and other visualization software. 13 (C 5 NH 12 + )

14  Iterative  Keyword: ITERATIVE  Solves the PCM electrostatic problem through a linear scaling iterative method using a Jacobi-like scheme  Advantageous when memory is limited.  Inversion  Keyword: INVERSION  Solve the PCM electrostatic problem to calculate polarization charges through the inversion matrix D with dimension of N tes xN tes  Gaussian 03 uses Inversion by default. 14

15  The original version of PCM  Electrostatics directly from the cavity model  Charges produces by discontinuity in the electric field across the boundary created by the cavity  Very sensitive to solute charge outside the cavity  Only single point calculations  No longer recommended 15

16  Default in Gaussian 03  Less sensitive to diffuse solute charge distributions  PCM + careful outlying charge corrections => IEFPCM 16

17  Uses the assumption that the cavity surface to be conductor-like  This assumption simplifies the solution of Poisson equation and calculation of the surface charges  Results can be outputted in COSMO RS format  Not recommended for solvents with low polarity  It is more efficient in iterative regime 17

18  Cavity formed using gas-phase static electronic isodensity surface (IPCM)  Less arbitrary than spheres on atoms  Cavity changes with electron density and environment  The default density value is 0.0004  only single point calculations  Self-Consistent Isodensity (SCIPCM)  iterations are folded in SCF  issues regarding scaling of charges still remain  References  J. Foresman, T.Keith, K. Wiberg, J. Snoonian, M. Frisch, J. Phys. Chem. 100,16098 (1996). 18

19 19 SCRF(Dipole,A0=5.5,eps=78.39) SCRF(IEFPCM) is the same as SCRF(PCM), or just SCRF SCRF(CPCM,Solvent=THF,Read) SCRF(IPCM) SCRF(SCIPCM)

20 20 %chk=pip-pcm #P HF/6-31g(d) SCRF(PCM,Solvent=Water,Read) test Piperidinium cation 1 N C 1 1.50977268 C 2 1.52365511 1 109.63925419 C 3 1.53136665 2 111.56508108 1 -55.04631728 C 1 1.50978576 2 113.42079276 3 57.07092348 C 4 1.53134037 3 110.99585756 2 54.90811126 H 1 1.00969298 5 109.64667654 6 -179.99768911 H 1 1.01028619 5 109.06107319 6 64.67690355 H 2 1.08151743 1 106.09798567 5 -64.03241054 H 2 1.08069845 1 107.09512052 5 179.68520816 H 3 1.08732966 2 109.45874935 1 67.33780856 H 3 1.08342937 2 107.81444282 1 -177.04873713 H 4 1.08661607 3 109.70973952 2 -66.50424273 H 4 1.08269752 3 109.4557835 2 176.38517116 H 5 1.08069728 1 107.09836585 2 -179.68240007 H 5 1.08151732 1 106.09918524 2 64.03563496 H 6 1.08732304 4 110.31444998 3 66.98445589 H 6 1.08344075 4 110.90163383 3 -175.10999479 PCMDOC ITERATIVE GEOMVIEW PCM solvation is requested. Solvent is Water. Additional PCM specific keywords are provided PCM specific keywords

21 21 SCF Done: E(RHF) = -250.669391936 A.U. after 6 cycles Convg = 0.7269D-05 -V/T = 2.0012 S**2 = 0.0000 -------------------------------------------------------------- Variational PCM results ======================= (a.u.) = -250.570493 (a.u.) = -250.669392 Total free energy in solution: with all non electrostatic terms (a.u.) = -250.662541 -------------------------------------------------------------- (Polarized solute)-Solvent (kcal/mol) = -62.06 -------------------------------------------------------------- Cavitation energy (kcal/mol) = 16.10 Dispersion energy (kcal/mol) = -12.61 Repulsion energy (kcal/mol) = 0.81 Total non electrostatic (kcal/mol) = 4.30 --------------------------------------------------------------

22 22

23 Method  G solv, kcal/mol SP SCRF(Dipole,A0=5.5)-30.6 SP SCRF(PCM)-56.0 SP SCRF(CPCM)-56.1 SP SCRF(IPCM)-59.4 SP SCRF(SCIPCM)-60.9 Opt SCRF(PCM)-56.3 Opt SCRF(CPCM)-56.4 Opt SCRF(SCIPCM)-61.1 Experiment-60.0 23 PCM cavity was constructed of 1006 tesserae Dipole, IPCM and SCIPCM results includes electrostatic effects only, sum of non-electrostatic is + 4.3 kcal/mol (PCM). QM: HF/6-31G(d)

24 24 Donor = 4-Biphenyl Acceptor = 2-Naphthyl Spacer: 5-a-androstane e  D  SA → DSA 

25 25 ET system Method to solve surface charges Memory,M b CPUsTime, min. Matrix inversion (default) 240192.5 640132 800131 1600130 1600422 Iterative 64128 640129 800127 1600129 400417.5 ROHF/6-31G(d,p) SP SCRF(IEFPCM, Solvent=THF) D  SA → DSA  D: 4-Biphenyl A: 2-Naphthyl S:5-  -androstane 87 atoms in total, 5158 tesserae created

26 26 Method to solve surface charges Memory,M b CPUsTime, min. Matrix inversion (default) 240129 640129 800128 1600128 1600419 Iterative 64116 640116 800116 1600116 80045.75 ROHF/6-31G(d,p) SP SCRF(СPCM, Solvent=THF) D  SA → DSA  D: 4-Biphenyl A: 2-Naphthyl S:5-  -androstane 87 atoms in total, 5158 tesserae created

27 27 In vacuo ROHF and UHF calculations fails to produce the precursor state. Altering of MOs does not help. Polarization field of solvent makes it possible to obtain solution (with solvent polarization effects included!) for both precursor and successor states  G = -7.7 kcal/mol (IEFPCM)  G = -9.6 kcal/mol (СPCM)  G = -2.7 kcal/mol (СPCM, optimization, 78 hrs.)  G = -5±1 kcal/mol (Experiment) Blue structure is the precursor, 4-biphenyl is planar Red structure is successor, 4-biphenyl dihedral angle is 42.9º using guess=alter option and altering order of HOMO and LUMO

28  What is  G and  G ≠ for the reaction?  What is the nature of the transition state?  How does solvent change the result? 28 NH 3 CH 3 ClNH 3 CH 3 + Cl 

29 Model G≠G≠ GG Gas43.7120.0 Onsager18.210.0 DPCM@Onsager24.2-21.0 CPCM24.8-21.5 Experiment – for CH 3 I Gas?110 Solution24-30 Energies in kcal/mol 29 NH 3 CH 3 ClNH 3 CH 3 + Cl 

30 ModelC-NC-ClH-N-CCl-C-H Gas1.7652.571110.678.7 Onsager2.2732.250112.694.2 CPCM2.1452.249110.392.6 30

31  Preliminary in vacuo calculations (geometry and wavefunction guess)  In many cases SP SCRF after Optimization in vacuo is enough  IEFPCM ( It is the default method in G03)  When memory is limited, or the system is large, the Iterative algorithm is faster and less demanding than Inversion  When time is crucial, CPCM is recommended under some conditions:  polar solvent;  keyword Iterative! 31


Download ppt "Dr. Ivan Rostov Australian National University, Canberra"

Similar presentations


Ads by Google