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Department of Chemistry

 
Portrait of asa10

The work of our group is primarily focused on the electron correlation problem - namely how to compute the correlation energy for an atom, molecule, or even solid, starting from a mean-field (say Hartree-Fock) description of the system. Our approach is to combine quantum chemical ideas with stochastic (Monte Carlo) techniques, which enable us to tackle problems which are very difficult to solve use standard quantum chemical techniques alone.

We are developing Quantum Monte Carlo algorithms adapted for electronic (and more generally Fermionic) problems by working in Slater determinant spaces. The central problem which is encountered is the infamous "Fermion sign problem", which results from electronic wavefunctions having both positive and negative amplitudes. Currently we are working on a novel population dynamics algorithm which propagates walkers in Slater determinant space according to a type of "stochastic cellular automaton" obeying simple rules. The movie on the home page of our research group website shows an evolving population of walkers of positive and negative sign settling on the FCI wavefunction of a nitrogen dimer in a minimal basis - an archetypal multireference system. The remarkable aspect of this dynamics is the spontaneous symmetry breaking caused by annhilation processes, allowing the exact nodal surface of the nitrogen molecule, as expressed by the CI coefficients, molecule to appear. No fixed-node approximation is applied.

Further animations of this method in action can be viewed here.

Publications

Are smooth pseudopotentials a good choice for representing short-range interactions?
P Jeszenszki, A Alavi, J Brand
– Physical Review A
(2019)
99,
033608
Compact numerical solutions to the two-dimensional repulsive Hubbard model obtained via nonunitary similarity transformations
W Dobrautz, H Luo, A Alavi
– Physical Review B
(2019)
99,
075119
Accelerating the convergence of exact diagonalization with the transcorrelated method: Quantum gas in one dimension with contact interactions
P Jeszenszki, H Luo, A Alavi, J Brand
– Physical Review A
(2018)
98,
ARTN 053627
Correlation energies of the high-density spin-polarized electron gas to meV accuracy
M Ruggeri, PL Rios, A Alavi
– Physical Review B
(2018)
98,
161105
Nonlinear biases, stochastically sampled effective Hamiltonians, and spectral functions in quantum Monte Carlo methods
NS Blunt, A Alavi, GH Booth
– Physical Review B
(2018)
98,
ARTN 085118
Time Propagation and Spectroscopy of Fermionic Systems Using a Stochastic Technique
K Guther, W Dobrautz, O Gunnarsson, A Alavi
– Physical review letters
(2018)
121,
056401
The Intricate Case of Tetramethyleneethane: A Full Configuration Interaction Quantum Monte Carlo Benchmark and Multireference Coupled Cluster Studies
L Veis, A Antalík, Ö Legeza, A Alavi, J Pittner
– J Chem Theory Comput
(2018)
14,
2439
Combining the Transcorrelated Method with Full Configuration Interaction Quantum Monte Carlo: Application to the Homogeneous Electron Gas
H Luo, A Alavi
– Journal of chemical theory and computation
(2018)
14,
1403
Density matrices in full configuration interaction quantum Monte Carlo: Excited states, transition dipole moments, and parallel distribution.
NS Blunt, GH Booth, A Alavi
– The Journal of chemical physics
(2017)
146,
244105
Stochastic multi-reference perturbation theory with application to the linearized coupled cluster method (vol 146, 044107, 2017)
G Jeanmairet, S Sharma, A Alavi
– The Journal of Chemical Physics
(2017)
146,
239901
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Research Group

Research Interest Group

Telephone number

01223 762877

Email address

asa10@cam.ac.uk