Search found 113 matches
- Fri Mar 09, 2018 11:48 am
- Forum: Quantum Monte Carlo
- Topic: DMC timestep bias asymptotic
- Replies: 17
- Views: 112680
Re: DMC timestep bias asymptotic
Dear Vladimir, One argument for the time-step bias in the energy being linear is that the time-step error in the DMC Green's function is O(tau^2), and hence time-step errors are introduced at a rate O(tau^2)/tau=O(tau) into the mixed wave function f ( R , t )=phi( R , t ).Psi( R ), where Psi( R ) is...
- Sat Jan 27, 2018 10:21 am
- Forum: Jobs
- Topic: Senior Lecturer in Condensed Matter Theory
- Replies: 0
- Views: 64836
Senior Lecturer in Condensed Matter Theory
Department of Physics, Lancaster University, UK Salary : £50,618 to £56,950 Closing Date : Sunday 25 February 2018 Interview Date : To be confirmed Reference : A2179 Lancaster University's Department of Physics seeks to appoint a full-time Senior Lecturer to enhance and complement our thriving acti...
- Wed Jan 03, 2018 4:41 pm
- Forum: The CASINO program
- Topic: Accelerated Metropolis Method
- Replies: 1
- Views: 28565
Re: Accelerated Metropolis Method
Dear Vladimir, I played around with "accelerated" Metropolis VMC methods in about 2002 and concluded that one can easily come up with transition probability densities that require fewer Monte Carlo iterations to achieve a given error bar; however, none of these methods was actually more ef...
- Sun Dec 31, 2017 10:55 pm
- Forum: The CASINO program
- Topic: parallel version breaks on multi determinant WFN
- Replies: 4
- Views: 39424
Re: parallel version breaks on multi determinant WFN
Dear Vladimir, Thanks very much for reporting the problem and sorry for any inconvenience. The bug was introduced in 2.13.650. The issue is that mdet_max_mods needs to be broadcast before it is used in READGW in gaussians.f90. I've attached the git patch that I've just sent to Mike. Happy New Year! ...
- Sat Dec 30, 2017 10:07 pm
- Forum: The CASINO program
- Topic: parallel version breaks on multi determinant WFN
- Replies: 4
- Views: 39424
Re: parallel version breaks on multi determinant WFN
Dear Vladimir,
Thanks for the report. Do you have an example that fails? (The MDET examples in CASINO/examples/TEST seem to work OK, at least with the gfortran and NAG compilers.)
Best wishes,
Neil.
Thanks for the report. Do you have an example that fails? (The MDET examples in CASINO/examples/TEST seem to work OK, at least with the gfortran and NAG compilers.)
Best wishes,
Neil.
- Mon Sep 04, 2017 12:39 pm
- Forum: The CASINO program
- Topic: Is CASINO QMC realy linear scaling?
- Replies: 1
- Views: 27707
Re: Is CASINO QMC realy linear scaling?
Dear Vladimir, Sadly it doesn't make CASINO scale linearly with problem size. The cost of evaluating the wave function (or calculating a local energy, etc.) is usually dominated by the cost of evaluating the Slater wave function. For a localised basis set (e.g., blips or Gaussians but not plane wave...
- Thu Aug 24, 2017 2:28 pm
- Forum: The CASINO program
- Topic: varmin gives NaN
- Replies: 12
- Views: 64884
Re: varmin gives NaN
Dear Katharina, Yes, sorry, I meant that it is usually best to aim for consistency in the cutoff lengths between different calculations when calculating energy differences or calculating results to be combined in some way. For example, when studying condensed matter I usually set the cutoff length f...
- Thu Aug 24, 2017 12:56 pm
- Forum: The CASINO program
- Topic: varmin gives NaN
- Replies: 12
- Views: 64884
Re: varmin gives NaN
To be honest I don't usually bother optimising cutoff lengths these days. It's usually more important to be consistent with one's choice of cutoff lengths. When an optimisation goes wrong try the following: reducing the number of parameters (can increase it again later); increasing the number of con...
- Sat Jul 29, 2017 6:44 pm
- Forum: Quantum Monte Carlo
- Topic: trial/guiding wave function optimisation for DMC
- Replies: 6
- Views: 35870
Re: trial/guiding wave function optimisation for DMC
Dear Vladimir,
Optimisation of the trial wave function by energy minimisation theoretically makes DMC more efficient than any other optimisation method. See David Ceperley's argument in J. Stat. Phys 43, 815 (1986).
Best wishes,
Neil.
Optimisation of the trial wave function by energy minimisation theoretically makes DMC more efficient than any other optimisation method. See David Ceperley's argument in J. Stat. Phys 43, 815 (1986).
Best wishes,
Neil.
- Thu Jun 15, 2017 1:55 pm
- Forum: Quantum Monte Carlo
- Topic: DMC energy
- Replies: 21
- Views: 93363
Re: DMC energy
Dear Vladimir, The optimised VMC time step is generally determined by the most important length scale, not necessarily the longest length scale in the system being studied. Fitting a sum of exponential decays to the DMC energy could in principle tell you about excited-state energies. However, these ...