Search found 113 matches

by Neil Drummond
Fri Nov 28, 2014 4:21 pm
Forum: The CASINO program
Topic: scaling of casino
Replies: 4
Views: 11217

Re: scaling of casino

Dear Katharina, The time should only depend weakly on the blip multiplicity. Usually the time spent evaluating blip orbitals is dominated by the time spent evaluating the blip functions themselves. (On the other hand, the memory requirements will increase rapidly with blip multiplicity.) The time ta...
by Neil Drummond
Mon Oct 06, 2014 9:56 pm
Forum: The CASINO program
Topic: Reblock convergence with large number of walkers
Replies: 1
Views: 8320

Re: Reblock convergence with large number of walkers

Dear Kayahan, For the DMC statistics accumulation stage, to achieve a given error bar you need to sample a given number of independent configurations. In principle the computational expense is the same, irrespective of whether you use a large population and a small number of steps or a small populat...
by Neil Drummond
Tue May 06, 2014 4:25 pm
Forum: The CASINO program
Topic: finite size corrections in 2D
Replies: 6
Views: 15770

Re: finite size corrections in 2D

Dear Dario, The relevant bit of code predates the finite-size paper by two years, suggesting that the finite-size correction to the exchange-correlation energy wasn't implemented in 2D because the expression for the correction wasn't known at the time. If you have accumulated the static structure fa...
by Neil Drummond
Tue May 06, 2014 3:53 pm
Forum: The CASINO program
Topic: finite size corrections in 2D
Replies: 6
Views: 15770

Re: finite size corrections in 2D

Dear Dario, Formulae for finite-size corrections in 2D - to both the interaction energy and the kinetic energy - can be found in N.D. Drummond et al. , Phys. Rev. B 78 , 125106 (2008). The leading-order correction to both the interaction energy and the kinetic energy is positive and scales as N ^(-1...
by Neil Drummond
Tue Mar 11, 2014 10:48 pm
Forum: The CASINO program
Topic: CASINO in a dielectric medium
Replies: 1
Views: 8739

Re: CASINO in a dielectric medium

Do you envisage calculations for a model system (pair of two-dimensional electron gases, with an effective interaction between the electrons)?

Modifying the form of the interaction between particles is straightforward, but would require a change to the code.

Best wishes,

Neil.
by Neil Drummond
Fri Nov 29, 2013 3:53 pm
Forum: The CASINO program
Topic: high vmc_ave_period and correlation less than 1
Replies: 1
Views: 7953

Re: high vmc_ave_period and correlation less than 1

Dear Varelse, If the correlation period is one step (it can't really be smaller) then you would expect the reblocked error bars to "start" in a plateau (i.e., you won't see the error bar rise with reblocking transformation before reaching the plateau). In principle it doesn't matter what b...
by Neil Drummond
Tue Nov 19, 2013 8:42 pm
Forum: The CASINO program
Topic: Rough estimate about speed of Casino
Replies: 4
Views: 14078

Re: Rough estimate about speed of Casino

Dear Amartya, If you are interested in an energy per atom then the CPU time for DMC statistics accumulation to achieve a given error bar is linear in the number of particles in the supercell. If you are interested in total energies, e.g., because you want to calculate points on a band structure, the...
by Neil Drummond
Tue Nov 19, 2013 5:46 pm
Forum: The CASINO program
Topic: Rough estimate about speed of Casino
Replies: 4
Views: 14078

Re: Rough estimate about speed of Casino

Dear Amartya, Depends on how exactly you perform your calculations. Let's assume you use a supercell containing about 400 electrons, a Slater-Jastrow wave function, a time step of 0.01 a.u. and 4 configurations per core, with 1000 cores, in your DMC calculations. You will probably need to carry out ...
by Neil Drummond
Fri Oct 25, 2013 9:31 pm
Forum: The CASINO program
Topic: Cutoff lengths in the Jastrow factor
Replies: 12
Views: 31324

Re: Cutoff lengths in the Jastrow factor

Dear Varelse, The cutoff length behaviour you describe seems a bit unusual; nevertheless every system is unique and, if the energy expectation value is going down, one cannot argue with the variational principle. If you are looking at similar systems then I would certainly make use of what you have ...
by Neil Drummond
Fri Sep 20, 2013 2:02 pm
Forum: The CASINO program
Topic: Jastrow optimisation, the default in 2.12
Replies: 15
Views: 37196

Re: Jastrow optimisation, the default in 2.12

Dear Philip,

I suggest using a 2x2x1 grid with inversion symmetry, which will allow a real wave function, for the optimisation of the Jastrow factor. You can then use that Jastrow factor for all offsets to your 2x2x1 grid of k vectors.

Best wishes,

Neil.