Search found 95 matches

by Neil Drummond
Fri Mar 09, 2018 4:16 pm
Forum: Quantum Monte Carlo
Topic: DMC timestep bias asymptotic
Replies: 14
Views: 42824

Re: DMC timestep bias asymptotic

The errors in the DMC Green's function, in f(R) and hence in the energy can be of either sign. In my experience time-step bias in the energy is usually, but not always, positive.

Best wishes,

Neil.
by Neil Drummond
Fri Mar 09, 2018 12:04 pm
Forum: Quantum Monte Carlo
Topic: electron-plasmon interaction
Replies: 1
Views: 6079

Re: electron-plasmon interaction

Dear Manuel,

Unfortunately this isn't readily available or implemented, and thought would be required...

Best wishes,

Neil.
by Neil Drummond
Fri Mar 09, 2018 11:48 am
Forum: Quantum Monte Carlo
Topic: DMC timestep bias asymptotic
Replies: 14
Views: 42824

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...
by Neil Drummond
Sat Jan 27, 2018 10:21 am
Forum: Jobs
Topic: Senior Lecturer in Condensed Matter Theory
Replies: 0
Views: 16641

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...
by Neil Drummond
Wed Jan 03, 2018 4:41 pm
Forum: The CASINO program
Topic: Accelerated Metropolis Method
Replies: 1
Views: 10372

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...
by Neil Drummond
Sun Dec 31, 2017 10:55 pm
Forum: The CASINO program
Topic: parallel version breaks on multi determinant WFN
Replies: 4
Views: 14699

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! ...
by Neil Drummond
Sat Dec 30, 2017 10:07 pm
Forum: The CASINO program
Topic: parallel version breaks on multi determinant WFN
Replies: 4
Views: 14699

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.
by Neil Drummond
Mon Sep 04, 2017 12:39 pm
Forum: The CASINO program
Topic: Is CASINO QMC realy linear scaling?
Replies: 1
Views: 10359

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...
by Neil Drummond
Thu Aug 24, 2017 2:28 pm
Forum: The CASINO program
Topic: varmin gives NaN
Replies: 12
Views: 27072

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...
by Neil Drummond
Thu Aug 24, 2017 12:56 pm
Forum: The CASINO program
Topic: varmin gives NaN
Replies: 12
Views: 27072

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...