Challenges and Hot Topics

John S. Tse

Department of Physics and Engineering Physics University of Saskatchewan, Saskatoon, Canada

SUPS, Madrid, 30th August, 2015

A brief introduction (what would one expect at high pressure)

Structures and structural principles

Pressure induced chemistry and photophysics

Disordered systems

Theory and computation

First result

“If you put a material in a diamond anvil cell, the chance is that you are going to observe something new”

A naive comment, IUCr High Pressure Workshop, Argonne National Laboratory, 1998

Nature, 410, 661 (2001) Phys. Rev. Lett., 87 ,215501 (2001)

First result

“If you put a material in a diamond anvil cell, the chance is that you are going to observe something new”

A naive comment, IUCr High Pressure Workshop, Argonne National Laboratory, 1998

1 bar = 6.24×10-7 eV/Å3

1 GPa = 6.24×10-3 eV/Å3

100 GPa = 0.624 eV/Å3

1000GPa = 6.24 eV/Å3

E(H…O) = 0.1 – 0.5 eV/mol E(O-H) = 5.1 3V/mol E(N-H) = 4.7 eV/mol E(C-H) = 4.3 eV/mol E(Si-H) = 3.0 eV/mol E(Sn-H) = 2.6 eV/mol

dissociation, structural instabiliity

1 bar ~ 1 atmosphere

Adopted from V. E. Fortov and V. B. Mintsev Russ. Chem. Rev. 82, 597-615 (2013).

Why?

Large change in electron density

New mode of “chemical” bonding

New structural types

Novel properties

The consequences

Hot Topic (1)

Hot Topic (2)

392 GPa

Solving scientific important problems

• High pressure is a versatile adjustable parameter

• Look for fundamental scientific problems

• Technical development - both experimental and theoretical

Hot Topic and Challenge: 1

Pressure induced chemical reactions

Photochemistry and Photophysics

A general structural principles

Synergy between theory and experiment

Strobel, et.al., Phys. Rev. Lett. 103, 065701 (2009)

“All of the electrons are involved and the role of high-pressure physics has been to force those nominally “valence” electrons into the regions between the nuclei. Eventually, relentless increase of pressure can literally strip away the traditionally “non-valence” electrons from the nuclei …”

Closed shell interactions - new type of chemical bond?

A SiH4-H2 molecular complex

288 atoms/200K/11GPa

NPT AIMD

0 10 20 30 4040

45

50

55

60

65

70 Expt

PBE

AM05

Vo

lum

e /

Å3

Pressure / GPa

4100 4200 4300 4400 45000

Vib

rati

on

al D

ensi

ty o

f Sta

tes

Frequency / cm-1

How the voids are filled

*

Donor-acceptor

W.L. Yim, J. S. Tse and T . Iitaka, Phys. Rev. Lett., 15, 21550 (2010)

Closed shell interactions

A gradual, pressure-induced change in bonding from van der Waals to ionic interactions near 50 GPa, forming aamorphous dinitrogen network containing ionized ammonia in a room-temperature analogue of the Haber–Bosch process. Hydrazine is recovered on decompression.

120 GPa

NPT simulations at 300 K

150 fs 150 0fs

Decompressed to 5 GPa

Pressure-induced Chemical Processes

P

Pressure-induced Chemical Processes

30 GPa and 500K

52SiO2:40CO2

SSZ-56

The mechanisms

Mechanisms

9 GPa

quench recovered at 0 GPa

Optimized structure at 9 GPa: P21 a = 4.389, b = 4.181, c = 5.983 Å, = 90.5o

Quenched melt 2000K, 23 GPa

5 10 15 20 25-0.5

0.0

0.5

1.0

1.5

E

nth

alpy (

eV)/

CO

2.S

iO2

Pressure (GPa)

CSiO4-[CO

2-III+Quartz]

CSiO4-[CO

2-III+Cristobalite]

Metastable phase

h

ffiif EUk 2

2 ffiif EUk 2

2

Photochemistry and Photophysics

ELF = 0.88

Li

Charge density

FeNa3

Role of electride? Why opn framework?

ELF = 0.88 Charge density and Maximum Entropy Method

2 4 6 8 10 12 14 16 18 20 22 24

100000

200000

300000

400000

500000

4.50 GPa

2.60 GPaDiffr

actio

n I

nte

nsity (

arb

. u

nits)

2(degrees)

1.77 GPa

0.4133 Å

5 10 15 20 25

25oC

= 0.41373 Å

Inte

nsi

ty

2 (degree)

GPa

0.12

0.56

1.60

3.00

3.90

4.80

5.70

6.90

8.00

Cs

Li

Challenge: accurate intensity measuement

J.S. Tse, et.al.,Sci. Adv., in press

Maximum entropy analysis

Slow, ramp compression from ~0-15 GPa using membrane apparatus • Search for possible metastable phase Ba III • Explore nucleation and crystal growth of

complex phase(s) of Ba IV

Time resolved x-ray diffraction

Analysis software, Artificial Intelligence

J.S. Smith and J.S. Tse (2014)

Hot Topic and Challenge 2

Disordered system

Hot topics: Pressure-induced poly(a)morphism transition

Non-cubic scaling law and negative thermal expansion

Model system for dense packing of binary spheres

H.Brouwer, PRE, 76, 041304 (2007) ; ibid. 78, 011303 (2008)

Why disordered systems so interesting?

Low q (momentum transfer) acoustic excitations, intermediate to long range correlation

NSLS-2 qmin ~ 0.5nm-1 E/E = 0.8 meV – 1.3 eV

ID-20 ESRF qmin ~0.2nm-1 E/E = 0.75 eV

Challenge : low q and high energy resolution

Opportunities

Si-

O c

oo

rdin

ati

on

nu

mb

er

Opportunities – structure of silica glass

K. Gilmore and J.S. Tse (2015)

Hot Topic and challenge 3

Theoretical development – better theory and computational methods

“transition pressures obtained from density-functional

theory exchange correlation functionals which neglect

vdW forces are greatly overestimated”

van der Waals functional for weak interactions

120 150 180 210 240 270 300

0

10

20

30

40

50

Pre

ssu

re (

GP

a)

Volume (A3)

LDA-only

PBE-only

PBEsol

Grimme-D2

PBE-TS

optB86b

DF2

Exp.

r(Br-Br)

Challenge: A density functional cover all range

• Particle Swarm Optimization

• Genetic algorithm

• Metadynamics

• Random search

• Basin hopping

Structure prediction

Methodologies

• Improve efficiency and reliability

• Ranking of lowest energy structures

• Transition path sampling

• Multivariate optimization • Temperature effect

Challenges

Drozdov, et.al. arXiv:1508.06224 (2015)

• Particle Swarm Optimization

• Genetic algorithm

• Metadynamics

• Random search

• Basin hopping

Structure prediction

Methodologies

• Improve efficiency and reliability

• Ranking of lowest energy structures

• Transition path sampling

• Multivariate optimization • Temperature effect

Challenges

Drozdov, et.al. arXiv:1508.06224 (2015)

• Particle Swarm Optimization

• Genetic algorithm

• Metadynamics

• Random search

• Basin hopping

Structure prediction

Methodologies

• Improve efficiency and reliability

• Ranking of lowest energy structures

• Transition path sampling

• Multivariate optimization • Temperature effect

Challenges

Drozdov, et.al. arXiv:1508.06224 (2015)

Fe (6000K) ~ 13 mPa s

300 GPa

Limitation of Quasiharmonic Approximation

Properties at high temperature and pressure

Transport properties: Electrical conductivity

Thermal conductivity

Viscosity

Elastic moduli

Static correlation – multi-determinant states?

Static correlation – multi-determinant states?

Static correlation – multi-determinant states?

Bethe-Salpeter Equation (BSE)

Hot Topic and Challenge 2

Pressure as an adjustable external variable

R

β≪0

W 2 W 2

W

> 0

PM

AFM/FM

covalent bond

Ueff =U - J

Metallization of single molecule crystal

Band gap tuning

Region I : Localized 4f state single determinant

Region II : mixed valence state two determinants

= 𝑐1… 4f7d0… + c2 … 4f6d1…

Region III : metallic state single determinant

I II III

Region I : Localized 4f state single determinant

Region II : mixed valence state two determinants

= 𝑐1… 4f7d0… + c2 … 4f6d1…

Region III : metallic state single determinant

I II III Hubbard LDA+U; Hybrid functional (HSE) ; model pseudopotential

??? Multi-reference - QMC

Standard density functional

Sheng, et.al. Nat. mat., 6.192 (2007) Zeng, et.al., PNAS, 106, 2515 (2009)

-8

-6

-4

-2

0

2

4

6

8

En

ergy

(eV

)

-8

-6

-4

-2

0

2

4

6

8

En

ergy

(eV

)

Eu2O3

| + = c1|… 4f7d0… + c2 … 4f6d1…

| - = c2|… 4f7d0… - c1 … 4f6d1…

4f75d0 4f65d1

|-

|+

Eu 2p (LII,III)

0.028e/Å3

Shortest O-O contact (d=2a*) : 1.8Å

Metallization density per O atom (Dm) : 0.107 /Å3

Metallization volume Vm = 1/(Dm )1/3 = 2.1 Å

(Dm)1/3 a* = 0.9/2.1 = 0.42

h

ffiif EUk 2

2 ffiif EUk 2

2