Concise Physical Chemistry

c20 JWBS043-Rogers September 13, 2010 11:29 Printer Name: Yet to Come

DENSITY FUNCTIONAL THEORY (DFT) 339

E[MP2/6-31G(d)

E[MP2/G3MP2Large]

E[QCISD(T)/6-31G(d)]

Post

Hartree-Fock

Basis Set

Energy

E[QCISD(T)/G3MP2Large

FIGURE 20.8 Additive extrapolations in the G3(MP2) scripted method.

Temperature= 298.150000 Pressure= 1.000000

E(ZPE)= 0.049406 E(Thermal)= 0.052749

E(QCISD(T))= -115.374855 E(Empiric)= -0.064953

DE(MP2)= -0.161818

G3MP2(0 K)= -115.552220 G3MP2 Energy= 115.548877

G3MP2 Enthalpy= -115.547933 G3MP2 Free Energy= -115.574944

1\1\GINC-DOUG\Mixed\G3MP2\G3MP2\C1H4O1\DROGERS\08-Jun-2009\0\\# g3mp2\

\methanol\\0,1\C,0,0.0185989192,0.032214273,0.0391675131\O,0,0.0052594

495,0.0091096338,1.4617939406\H,0,1.0367987363,0.0123972426,-0.3682155

629\H,0,-0.5076630411,0.9040926655,-0.3682155629\H,0,-0.5013614095,-0.

8683834341,-0.2863534272\H,0,0.4651982827,0.8057470613,1.7693787775\\V

ersion=AM64L-G03RevD.01\State=1-A'\MP2/6-31G(d)=-115.3461339\QCISD(T)/

6-31G(d)=-115.3748547\MP2/GTMP2Large=-115.5079522\G3MP2=-115.5522202

FILE 20.11 Partial GAUSSIAN G3(MP2) output. (G3(MP2) is a slightly simplified version

of G3.)

20.18 DENSITY FUNCTIONAL THEORY (DFT)

DFT methods are quite fast relative to G3 and G3 (MP2) scripted molecular orbital

model chemistries. For this reason they have enjoyed popularity among computational

chemists working on practical problems. Density functional theory is based on the

fact that the average energy of an electron in an atom or a molecule is a function

of its probability densityρin the vicinity of the nucleus or nuclei, andρis a

function of its position in space. A function of a function is afunctional.DFT

methods are largely empirical, containing adjustable parameters, though each rests

on a reasonable theoretical model. One of the most accurate functionals, devised by

Becke (1932) and by Lee, Yang, and Parr in 1988 is denoted BLYP. The BLYP method