Density-functional methods for electronic systems at ...

Density-functional methods for electronic systemsat finite temperatures

Andreas Gorling, Max Greiner, Hannes Schulz, Patrick Bleiziffer,and Andreas Heßelmann

Lehrstuhl fur Theoretische ChemieUniversitat Erlangen–Nurnberg

J. Gebhardt, G. Gebhardt, T. Gimon, W. Hieringer, C. Neiß, I. Nikiforidis,K.-G. Warnick, T. Wolfle

A. Gorling (University Erlangen–Nurnberg) Los Angeles 2012 1 / 36

Overview

1 IntroductionElectronic structures at finite temperatures with DFTOrbital-dependent functionals

2 Exact-exchange (EXX) Kohn-Sham methods

3 Finite-temperature EXX Kohn-Sham methodsElectronic structure methods for grand canonical ensemblesKohn-Sham formalism for finite temperaturesFinite-temperature EXX-KS methodExamples for applications

4 Direct RPA and EXXRPA correlation energyFluctuation dissipation theorem for DFT correlation energyEXXRPA methodsPerformance of EXXRPA methods

5 Literature


Electronic structures at finitetemperatures with DFT

Finite-temperature density-functional theoryDFT for grand canonical ensembles

Problem: µ- and T -dependent exchange-correlation functionals required

Approach: Orbital-dependent, finite-temperature exchange-correlation functionals

First step: Temperature-dependent exact-exchange formalism,i.e., exchange energy and Kohn-Sham exchange potential are treated exactly


Orbital-dependent functionalsHistoric development of DFT

Ground state energy of an electronic systemE0 = Ts + U + Ex + Ec +

∫dr vnuc(r)ρ(r)

Thomas-Fermi-Dirac

E0 = Ts[ρ]+ U [ρ] +Ex[ρ] + Ec[ρ]+∫dr vnuc(r)ρ(r)

δE/δρ(r) = µ

Conventional Kohn-Sham

E0 = Ts[φi]+ U [ρ] +Ex[ρ] + Ec[ρ]+∫dr vnuc(r)ρ(r)

[T + vnuc + vH + vx + vc]φi = εiφi

Kohn-Sham with orbital dependent functionals

E0 = Ts[φi]+U [ρ]+Ex[φi] +Ec[φi]+∫dr vnuc(r)ρ(r)

[T + vnuc + vH + vx + vc]φi = εiφi


Exact treatment of KS exchangeOEP equation

Exchange energy

Ex = −1

2

occ.∑

i,j

∫dr dr′

φi(r′)φj(r

′)φj(r)φi(r)

|r′ − r|

Exchange potential vx(~r) =δEx[φi]δρ(~r)∫

dr′ χs(r, r′) vx(r

′) = t(r)

KS response function χs(r, r′) =

δρ(r)

δvs(r′)= 4

occ.∑

i

unocc.∑

a

φi(r)φa(r)φa(r′)φi(r′)

εi − εa

t(r) =δExδvs(r)

= 4

occ.∑

i

unocc.∑

a

φi(r)φa(r)⟨a|vNL

x |i⟩

εi − εa

Plane wave methods for solid numerically stableGaussian basis set methods for molecules numerically demanding


Exact-exchange Gaussian basis set KS method

Auxiliary basis set: Electrostatic potential of Gaussian functions

vx(r) =∑

k

vx,k fk(r) with fk(r) =

∫dr′ gk(r′)/|r− r′|

Incorporation of exact conditions to treat asymptotic of vx(r)∫dr ρx(r) = −1 with ρx(r) =

∑

k

vx,k gk(r)

〈φHOMO|vx|φHOMO〉 = 〈φHOMO|vNLx |φHOMO〉

Construction and balancing scheme for auxiliary and orbital basis sets,orbital basis set needs to be converged for given auxiliary basis set,uncontracted orbital basis sets required

JCP 127, 054102 (2007)

By preprocessing of auxiliary basis set and singular value decomposition ofresponse function, EXX calculations with standard contracted orbital basis sets(aug-cc-pCVQZ) possibleA. Gorling (University Erlangen–Nurnberg) Los Angeles 2012 6 / 36

EXX vs. GGA (PBE) orbitals of methane

2 t2u −2.934 eV

3 a1g −4.438 eV

1 t2u −14.724 eV

2 a1g −22.437 eV

-20

-15

-10

-5

0

2 t2u +0.533 eV

3 a1g −0.396 eV

1 t2u −9.448 eV

2 a1g −17.054 eV

contour value 0.032A. Gorling (University Erlangen–Nurnberg) Los Angeles 2012 7 / 36

EXX vs. GGA (PBE) orbitals of methane

2 t2u −2.934 eV

3 a1g −4.438 eV

1 t2u −14.724 eV

2 a1g −22.437 eV

-20

-15

-10

-5

0

2 t2u +0.533 eV

3 a1g −0.396 eV

1 t2u −9.448 eV

2 a1g −17.054 eV

contour value 0.013A. Gorling (University Erlangen–Nurnberg) Los Angeles 2012 8 / 36

Band gaps of semiconductors

FLAPW vs. PP EXX band gaps

EXX+VWNc Exp.FLAPWa PPb

Si Γ→ Γ 3.21 3.26 3.4Γ→ L 2.28 2.35 2.4Γ→ X 1.44 1.50

SiC Γ→ Γ 7.24 7.37Γ→ L 6.21 6.30Γ→ X 2.44 2.52 2.42

Ge Γ→ Γ 1.21 1.28 1.0Γ→ L 0.94 1.01 0.7Γ→ X 1.28 1.34 1.3

GeAs Γ→ Γ 1.74 1.82 1.63Γ→ L 1.86 1.93Γ→ X 2.12 2.15 2.18

C Γ→ Γ 6.26 6.28 7.3Γ→ L 9.16 9.18Γ→ X 5.33 5.43

aPRB 83, 045105 (2011)bPRB 59, 10031 (1997)


Summary EXX-KS method

EXX-KS methods solve the problem of Coulomb self-interactions and,in contrast to GGA-KS methods, yield qualitatively correct KS orbitaland eigenvalue spectra.

EXX orbitals and eigenvalues are well-suited as input for TDDFTmethods. Problem of treating excitations with Rydberg character issolved.

Correlation functional supplementing exact treatment of exchangerequired


Electronic structure methods forgrand canonical ensembles

Electronic Schrodinger equation: [T + Vee + v]ΨN,n = EN,nΨN,n

T = 0 finite T

EN,0 = minΨ→N

E[Ψ] Ωv,T,µ = minΓ

Ω[Γ]

E[Ψ] = 〈Ψ|H|Ψ〉 Ω[Γ] = Tr Γ[H + kT ln Γ− µN

]

EN,0 = E[Ψ0] Ωv,T,µ = Ω[Γv,T,µ]

HΨ0 = EN,0Ψ0 Γv,T,µ =∑

N

∑

n

exp[(−1/kT )(EN,n − µN)]

Zv,T,µ|ΨN,n〉〈ΨN,n|

Zv,T,µ =∑

N

∑

n

exp[(−1/kT )(EN,n − µN)]


Finite-temperature Kohn-Sham formalism

T = 0

Φ0 ←→ T + vs ←→ ρ0 ←→ T + Vee + v ←→ Ψ0

vS(r) = v(r) + vH ([ρ0]; r) + vxc ([ρ0]; r)

finite T

ΓKSvS ,T,µ ←→ T + vs ←→ ρv,T,µ ←→ T + Vee + v ←→ Γv,T,µ

vs(r) = v(r) + vH ([ρv,T,µ]; r) + vxc ([ρv,T,µ], T, r)


Basic density-functionals forgrand canonical ensembles

T = 0 finite T

F [ρ] = minΨ→ρ

〈Ψ|T + Vee|Ψ〉

→ Ψ[ρ]

F [ρ, T ] = minΓ→ρ

Tr Γ [T + Vee + kT ln Γ]

→ Γ[ρ, T ]

Ts[ρ] = minΨ→ρ

〈Ψ|T |Ψ〉

→ Φ[ρ]

Ts[ρ, T ] = minΓ→ρ

Tr Γ [T + kT ln Γ]

→ ΓKS[ρ, T ]

U [ρ] + Ex[ρ] = 〈Φ|Vee|Φ〉U [ρ] + Ex[ρ, T ] = Tr ΓKS[ρ, T ]Vee

Ec[ρ] = F [ρ]− Ts[ρ]− U [ρ]− Ex[ρ]

Ec[ρ, T ] = F [ρ, T ]− Ts[ρ, T ]− U [ρ]− Ex[ρ, T ]


Temperature-dependentexact-exchange energy

[T + vs]ΦN,n = EKSN,nΦN,n

ΓKSvs,T,µ=

∑

N

∑

n

exp[(−1/kT )(EKSN,n− µN)]

ZKSvs,T,µ|ΦN,n〉〈ΦN,n|

Ts = Tr ΓKSvs,T,µ[T+k T ln ΓKS

vs,T,µ]=∑

i

[fi〈i|− 1

2~∇2|i〉+ kT [fi lnfi + (1−fi) ln(1−fi)]

]

U + Ex = Tr ΓKSvs,T,µVee =

1

2

∑

i

∑

j

gij [〈ij|ij〉 − 〈ij|ji〉]

gij = fi fj fi =1

1 + e(1/kT )(εi−µ)


Temperature-dependent exact-exchange potential

OEP equation

∫dr′ Xs(T,N, r, r

′) vx(T,N, r, r′) = tx(T,N, r)

KS response function

Xs(T,N, r, r′) =

δρ(r)

δvs(r′)

=∑

i

fi∑

j 6=i

[φ†i (r)φj(r)φ†j(r

′)φi(r′)

εi − εj+ c.c.

]+∑

i

φ†i(r)φi(r)δfi

δvs(r′)

Right-hand side

tx(T,N, r)=∑

i

fi∑

j 6=i

[〈φi|vNL

x |φj〉φ†j(r)φi(r)

εi − εj+ c.c.

]+∑

i

〈φi| vNLx |φi〉

δfiδvs(r)


Test application bulk aluminum I

Free energy A = E − TS for bulk Al (fcc lattice, 6×6×6 k-points)

-54

-53

-52

-51

-50

-49

-48

1 2 3 4 5 6 7 8

A[eV

]

Volume [× exp. Vol. (293 K)]

293 K10000 K30000 K50000 K70000 K


Test application bulk aluminum II

Contributions to free energy A = E − TS

-54

-53

-52

-51

-50

-49

-48

1 2 3 4 5 6 7 8

A[eV]


293 K10000 K30000 K50000 K70000 K

-35

-30

-25

-20

-15

-10

-5

1 2 3 4 5 6 7 8

-T*S

[eV]


293 K10000 K30000 K50000 K70000 K

-55

-50

-45

-40

-35

-30

-25

-20

1 2 3 4 5 6 7 8

E total[eV]


293 K10000 K30000 K50000 K70000 K

-16

-14

-12

-10

-8

-6

-4

-2

1 2 3 4 5 6 7 8

E X[eV]


293 K10000 K30000 K50000 K70000 K


Test application bulk aluminum III

Band structures of aluminum

exp. Vol. (293 K)

-15

-10

-5

0

5

10

15

20

25

30

35

W L Γ X W K

ε i[eV]

293 K30000 K70000 K

5.1 × exp. Vol. (293 K)

-5

0

5

10

15

20

W L Γ X W K

ε i[eV]

293 K30000 K70000 K

0

0.2

0.4

0.6

0.81

-20

-10

010

2030

f(εi)

ε i−µ

[eV]f

(εi)=

1

1+exp(

1kBT(ε

i−µ))

293

K30

000

K70

000

K


Summarytemperature-dependent EXX method

Enables exact treatment of temperature in electronic structure calculationsat exchange level

Correlation functional supplementing exact treatment of exchange required

What can we learn from electronic structure calculations at hightemperatures? (Would inclusion of noncollinear spin, spin-orbitinteractions, or magnetic fields be of interest?)


Adiabatic-connection fluctuation-dissipationtheorem for DFT correlation energy I

Ec =−1

2π

∫ 1

0

dα

∫drdr′

1

|r− r′|

∫ ∞

0

dω[χα(r, r′, iω) − χ0(r, r′, iω)

]

Integration of response functions along complex frequencies

−1

2π

∫ ∞

0

dω

∫dr dr′g(r, r′) χα(r, r′, iω) =

=

∫dr dr′ g(r, r′)

[ρα2 (r, r′) − 1

2ρ(r)ρ(r′) + ρ(r)δ(r− r′)

]

∞∫

0

dωa

a2 + ω2=π

2later on g(r, r′) =

1

|r− r′|

χα(r, r′, iω) = −2∑

n 6=0

En − E0

(En − E0)2 + ω2〈Ψα

0 |ρ(r)|Ψαn〉〈Ψα

n|ρ(r′)|Ψα0 〉

Vc(α) =⟨Ψ0(α)|Vee|Ψ0(α)

⟩−⟨Φ0|Vee|Φ0

⟩


Adiabatic-connection fluctuation-dissipationtheorem for DFT correlation energy II

Ec =−1

2π

∫ 1

0

dα

∫drdr′

1

|r− r′|

∫ ∞0

dω[χα(r, r′, iω) − χ0(r, r′, iω)

]

Integration along adiabatic connection

Ec =

1∫0

dα Vc(α) with Vc(α) =⟨

Ψ0(α)|Vee|Ψ0(α)⟩−⟨

Φ0|Vee|Φ0

⟩Required input quantities are χ0(r, r′, iω) and χα(r, r′, iω)

KS response function χ0(r, r′, iω)

χ0(r, r′, iω) = −4occ∑i

unocc∑a

εaiε2ai + ω2

ϕi(r)ϕa(r)ϕa(r′)ϕi(r′)

Response functions χα(r, r′, iω) from EXX-TDDFT


Exact frequency-dependent exchange kernel

OEP-like equation for sum fHx(ω, r, r′) of Coulomb and EXX kernel∫

dr′′∫dr′′′ X0(r, r′′, ω) fHx(ω, r

′′, r′′′) X0(r′′′, r′, ω) = hHx(ω, r, r′)

withhHx(ω, r, r

′) = 14Yᵀ(r)λ(ω) [A + B + ∆]λ(ω)Y(r′)

+ ω2 14Yᵀ(r)λ(ω)ε−1 [A + B + ∆] ε−1λ(ω)Y(r)

+∑i

∑j

∑a

Yia(r)λia(ω)

⟨a|vNL

x − vx|j⟩

εa − εjφi(r)φj(r) + · · ·

+∑a

∑b

∑i

Yia(r)λia(ω)

⟨b|vNL

x − vx|i⟩

εb − εiφa(r)φb(r) + · · ·

Aia,jb = 2(ai|jb)− (ab|ji) Bia,jb = 2(ai|bj)− (aj|bi)∆ia,jb = δij 〈ϕa|vNL

x − vx|ϕb〉 − δab 〈ϕi|vNLx − vx|ϕj〉

λia,jb = δia,jb−4εiaε2ia+ω2 εia,jb = δia,jb εia = δia,jb(εa − εi)

Yia(r) = φi(r)φa(a)

hH(r, r′, ω) = Yᵀ(r)λ(ω) C λ(ω)Y(r) with Cia,jb = (ia|jb)A. Gorling (University Erlangen–Nurnberg) Los Angeles 2012 22 / 36

RI-EXXRPA method I

Ec =−1

2π

∫ ∞0

dω

∫ 1

0

dα

∫drdr′

1

|r− r′|[χα(r, r′, iω) − χ0(r, r′, iω)

]Representation of χα(iω), hx(iω) in RI basis set with respect to Coulomb norm

Xα = [1− αX0FHx]−1 X0 ⇒ Xα = X0 [X0 − αHHc]

−1 X0

(using FHx = X−10 HHcX

−10 )

Ec =−1

2π

∫ ∞0

dω

∫ 1

0

dα Tr[S−1 X0 [X0 − αH]−1X0 − S−1X0

]

Orthonormalize RI basis set, i.e. make S = E, and use Xα = −(−Xα)12 (−Xα)

12

Ec =−1

2π

∫ ∞0

dω

∫ 1

0

dα Tr

[(−X0)

12

[−1− α(−X0)−

12 H(−X0)−

12

]−1

(−X0)12 −X0

]with

X0(iω) = Dᵀλ(iω)D with Dia,h = (ϕiϕa|fh)Coul and λia,jb = δia,jb−4εiaε2ia + ω2

and

H(iω) = 14

DTλ(iω) [A+B+∆]λ(iω)D + (iω)2 14

DTλ(iω) ε−1[A+B+∆] ε−1 λ(iω)D

+ W1(iω) + WT1 (iω) + W2(iω) + WT

2 (iω)


RI-EXXRPA method II

Ec =−1

2π

∫ ∞0

dω

∫ 1

0

dα Tr

[(−X0)

12

[1− α(−X0)−

12 H(−X0)−

12

]−1

(−X0)12 − X0

]

Analytic integration over coupling constant

Ec =−1

2π

∫ ∞0

dω Tr[(−X0(iω))

12 U(iω)

(−τ−1(iω) ln[|1 + τ (iω)|]+1

)U(iω)T (−X0(iω))

12

]with

(−X0(iω))12 H(iω)(−X0(iω))

12 = U(iω) τ (iω) Uᵀ(iω)

Complete exchange kernel can be treated (RI-EXXRPA+)

N5 scaling


RI2-dRPA method

RI-EXXRPA

Ec =−1

2π

∫ ∞0

dω

∫ 1

0

dα Tr

[(−X0)

12

[1− α(−X0)−

12 H(−X0)−

12

]−1

(−X0)12 − X0

]

For dRPA, with second RI approximation and S = E, H simplifies to

H = X0X0

With spectral representation X0(iω) = −V(iω)σ(iω) V>(iω)

Ec =1

2π

∫ ∞0

dω Tr [ln[1 + σ(iω)]− σ(iω)]

Only KS response function X0(iω) required

N4 scaling


Results EXXRPA correlation methods I

Deviations of total energies from CCSD(T) energies, ∆E = EMethod − ECCSD(T)

Orbital basis: aug-cc-pVQZ RI basis: aug-cc-pVQZ

OEP (EXX) balanced uncontracted basis sets

-5

0

5

10

15

20

25

30

35

H2

H2 O

H2 O

2

CO

CO

2

NH

3

CH

4

C2 H

2

C2 H

4

C2 H

6

CH

3 OH

C2 H

5 OH

HC

HO

HN

CO

HC

OO

H

C2 H

4 O

CH

3 CH

O

H2 C

CO

HC

ON

H2

HC

OO

CH

3

NH

2 CO

NH

2

∆ E

[kca

l/m

ol]

CCSDMP2

EXXRPARI-EXXRPA

RI-EXXRPA+

0

10

20

30

40

50

60

70

80

90

100

110

120

CCSD

MP2

B3LYP

EXXRPA

RI-EXXR

PA

RI-EXXR

PA+

RI-dR

PA

RM

S [

kca

l/m

ol]


Results EXXRPA correlation methods II

Deviations of total energies from CCSD(T) energies, ∆E = EMethod − ECCSD(T)

Orbital basis: aug-cc-pCVQZ RI basis: aug-cc-pV5Z

OEP (EXX) basis sets equal to RPA basis sets

-5

0

5

10

15

20

25

30

35

H2

H2 O

H2 O

2

CO

CO

2

NH

3

CH

4

C2 H

2

C2 H

4

C2 H

6

CH

3 OH

C2 H

5 OH

HC

HO

HN

CO

HC

OO

H

C2 H

4 O

CH

3 CH

O

H2 C

CO

HC

ON

H2

HC

OO

CH

3

NH

2 CO

NH

2

∆ E

[kca

l/m

ol]

CCSDMP2

RI-EXXRPA+RI-EXXRPA

RI-EXX*RPA+

0 10 20 30 40 50 60 70 80 90

100 110 120

CCSD

MP2

RI-EXXR

PA

RI-EXXR

PA+

RI-EXX*R

PA+

RM

S [kcal/m

ol]

? OEP (EXX) balanced uncontracted basis sets


Results EXXRPA correlation methods III

Deviations of reaction energies from CCSD(T) reaction energies

Orbital basis: aug-cc-pVQZRI basis: aug-cc-pVQZ

OEP (EXX) balanced uncontracted basis sets

0

0.5

1

1.5

2

2.5

3

3.5

CCSD

MP2

B3LYP

EXXRPA

RI-EXXR

PA

RI-EXXR

PA+

RI-dR

PA

RM

S [

kca

l/m

ol]

Orbital basis: aug-cc-pCVQZRI basis: aug-cc-pV5Z

OEP (EXX) basis sets equal to RPA basis sets

0

0.5

1

1.5

2

2.5

3

3.5

CCSD

MP2

RI-EXXR

PA

RI-EXXR

PA+

RI-EXX *R

PA+

RM

S [

kca

l/m

ol]

? OEP (EXX) balanced uncontracted basis sets


Dissociation of H2

basis set: aug-cc-pVQZ

0 2 4 6 8 10 12 14 16 18 20r(H-H) [a0]

-1.1

-1

-0.9

-0.8

-0.7

-0.6en

ergy

[a.u

.]HF/EXXCIHF-RPAEXX-RPA

Dissociation limit of other molecules (CO, N2, etc.) is also treated correctly


Coupling constant integrand

Ec =1∫0

dα Vc(α)

-0.25

-0.2

-0.15

-0.1

-0.05

0

Vc(

α) [a

.u.]

r=1.4 a0r=6.0 a0r=10.0 a0r=20.0 a0r=30.0 a0

0 0.2 0.4 0.6 0.8 1coupling strength

-0.25

-0.2

-0.15

-0.1

-0.05

0

Vc(

α) [a

.u.]

HF-RPA

EXX-RPA

Vc(α)

-0.25

-0.2

-0.15

-0.1

-0.05

0

VcH

L (α)

[a.u

.]

r=1.4 a0r=6.0 a0r=10.0 a0r=20.0 a0r=30.0 a0

0 0.2 0.4 0.6 0.8 1coupling strength

-0.25

-0.2

-0.15

-0.1

-0.05

0

VcH

L (α)

[a.u

.]

HF-RPA

EXX-RPA

−(ia|ia)

V HLc (α)


Dissociation of N2

-109.4

-109.2

-109

-108.8

-108.6

-108.4

-108.2

-108

1.5 2 2.5 3 3.5 4 4.5 5 5.5

Energ

y [hart

ree]

r [bohr]

Orbital basis: avtz RI basis: avtz

HFEXX

CCSDRI-EXX-RPA

Special treatment of singularity in ω-Integrand ( −τ−1 ln [ |1 + τ (iω)| ] + 1 )


Twisting of ethene

Orbital basis: avqz RI basis: avqz

-78.6

-78.5

-78.4

-78.3

-78.2

-78.1

-78

-77.9

-77.8

0 20 40 60 80 100 120 140 160 180

En

erg

y [

Ha

rtre

e]

Torsion angle [degree]

HFEXX

CCSD

B3LYPRI-EXXRPA+

MCSCF


RI-EXXRPA for noncovalent bonds

Binding energies in kcal/mol

Complex Basis Reference RI-EXXRPA RI-EXXRPA+ RI-dRPA TPSS-RI-dRPA MP2 F12-CCSD

(NH3)2 3 2.54 2.76 2.33 3.004 2.61 2.83 2.46 3.11

CBS 3.15 2.70 2.92 2.58 2.74 3.18 2.88(H2O)2 3 4.29 4.55 3.73 4.72

4 4.60 4.86 4.24 5.02CBS 5.07 4.81 5.06 4.59 4.52 5.21 4.74

(HCONH2)2 3 14.87 15.27 13.43 15.084 15.42 15.84 14.23 15.57

CBS 16.11 15.77 16.21 15.28 15.42 15.86 15.28(HCOOH)2 3 17.40 17.90 15.25 17.61

4 18.06 18.46 16.24 18.23CBS 18.81 18.50 18.81 16.91 17.91 18.61 17.92

(C2H4)2 3 1.04 1.14 0.93 1.474 1.13 1.24 1.04 1.55

CBS 1.48 1.19 1.33 1.13 1.20 1.60 1.14C2H4···C2H2 3 1.34 1.45 1.21 1.59

4 1.37 1.46 1.26 1.64CBS 1.50 1.41 1.49 1.31 1.27 1.67 1.31

(CH4)2 3 0.30 0.37 0.29 0.464 0.34 0.36 0.33 0.48

CBS 0.53 0.36 0.34 0.35 0.40 0.49 0.41RMS 3 0.83 0.55 1.80 0.61RMS 4 0.50 0.25 1.29 0.31RMS CBS 0.29 0.13 0.94 0.52 0.15 0.51

– Geometries from test set of Jurecka, P.; Sponer, J.; Cerny, J.; Hobza, P.; Phys. Chem. Chem. Phys. 2006, 8, 1985– Reference: CBS CCSD(T) values from Takatani, T.; Hohenstein, E. G.; Malagoli, M.; Marshall, M. S.; Sherrill, C. D.; J. Chem. Phys. 2010, 132, 144104


EXX-RPA vs. HF based RPA

Deviations of reaction energies (RMS) from CCSD(T)

HFdRPA

SOSEX

HF-RPA

EXX-RPA

0

5

10

15

20

25

30

RM

S [k

cal/m

ol]

C2H2+H2 → C2H4

C2H4+H2 → C2H6

C2H6+H2 → 2CH4

CO+H2 → H2COH2CO+H2 → CH3OHH2O2+H2 → 2H2OC2H2+H2O → CH3CHOC2H4+H2O → C2H5OHCH3CHO+H2 → C2H5OHCO+NH3 → HCONH2

CO+H2O → CO2+H2

HNCO+NH3 → NH2CONH2

CH3OH+CO → HCOOCH3

CO+H2O2 → CO2+H2O

rCCD and SzOst-RPA yield distinctively larger deviations(larger deviations than HF)


Summary EXX-RPA

EXX-RPA correlation functional combines accuracy at equilibriumgeometries with a correct description of dissociation (static correlation)and a highly accurate treatment of VdW interactions

Promising starting point for further developments, e.g. inclusion ofcorrelation in KS potential or in kernel

Generalization to finite temperatures

Orbital-dependent functionals open up fascinating new possibilities in DFT


Literature

EXX for solids

Phys. Rev. Lett. 79, 2089 (1997) Phys. Rev. B 83, 045105 (2011)

finite-temperature EXX

Phys. Rev. B 81, 155119 (2010)

EXX for molecules

Phys. Rev. Lett. 83, 5459 (1999) J. Chem. Phys. 128, 104104 (2008)

TDEXX

Phys. Rev. A 80, 012507 (2009)Phys. Rev. Lett. 102, 233003 (2009)

Int. J. Quantum. Chem. 110, 2202 (2010)J. Chem. Phys. 134, 034120 (2011)

EXX-RPA

Mol. Phys. 108, 359 (2010)Mol. Phys. 109, 2473 (2011) Review

Phys. Rev. Lett. 106, 093001 (2011)J. Chem. Phys. 136, 134102 (2012)


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