The CASINO forum

Hello Mike I kept thinking about the elegance and the following thought came to me: If one can convert an orbital basis in the MOLDEN file from GTO back to STO and keep MO coefficients intact, could he benefit from this in VMC & DMC calculations and especially in the application of backflow proc...

Thanks Neil for the detailed explanation.

Сan you from such simple reasoning predict the sign of time step bias? Suppose that nodal surface is exact but trial WFN isn't.

As you can see from my plots time step error has negative sign.

Best Vladimir.

Vladimir, Thanks for your reply. I'm having a hard time chasing up what exactly has gone into the "exact energy" quoted in the earlier referenced PRE. For example, can you find where the experimental atomization energy of N_2 used to form the electronic ground state energy actually came f...

Also, you can have a fixed node error. If you are not working with the full wave function that gave the reference result in the first place (and I think that the value you cite was obtained by CCSDT), DMC may well also give an energy that is higher than the value from the "standard" quant...

Vladimir, I'm not sure what you are asking here. You're ground state energy is: -109.542(1) a.u., whilst the exact value (from Ref. 38 of the quoted PRE article) is -109.5421 a.u. These two are consistent with each other (at the level of statistical significance you are working), and your VMC energ...

Hello CASINO developers I'm using the QChem program to get trial WFN Qchem has “valence” active space methods VOD which allows you to get WFN and T2-amplitudes to construct CASINO input https://www.q-chem.com/qchem-website/manual/qchem43_manual/sect-ccactive.html When I create VOD single determinant...

Hello Cyrus I just read the article and want to note that in the case of single determinant WFN for Be atom and Be2 molecule which are known to give the wrong topology of nodal surface DMC time step bias no longer linear I applied polynomial interpolation be_be2.png E(Be) = -0.022459*x^1.5 - 0.01044...

If you look at Fig. 13 of Umrigar, Nightingale, Runge, J. Chem. Phys. 1993, you will see that it is nearly quadratic near tau=0. I do not know of a theoretical argument for the behaviour of the time-step error. What is the x-scale on your plots? Cyrus X scale is time step divided by τ = 1/(3Z^2), w...

Hello everyone who does DMC calculations. I calculated the time step bias dependence for simple full electron systems like H-Cl atoms and some diatomic. I've found that small time step asymptotic is rather quadratic than linear whereas large time step asymptotic is linear in some cases. For example ...

Hello CASINO developers. I wonder why the CASINO uses a spherical representation for the gaussian basic functions, while the сartesian representation requires a smaller number of computations to find both the values, derivatives and Laplacian etc. There is no difference only for S and P the orbitals...