We investigate the properties of norm-conserving pseudopotentials (effective core potentials) generated by inversion of the Hartree-Fock equations. In particular, we investigate the asymptotic behavior as r-->infinity and find that such pseudopotentials are nonlocal over all space, apart from a few special cases such as H and He. Such extreme nonlocality leads to a lack of transferability and, within periodic boundary conditions, an undefined total energy. The extreme nonlocality must therefore be removed, and we argue that the best way to accomplish this is a minor relaxation of the norm-conservation condition. This is implemented, and pseudopotentials for the atoms H-Ar are constructed and tested.

We report smooth relativistic Hartree-Fock pseudopotentials (also known as averaged relativistic effective potentials or AREPs) and spin-orbit operators for the atoms H to Ba and Lu to Hg. We remove the unphysical extremely non-local behaviour resulting from the exchange interaction in a controlled manner, and represent the resulting pseudopotentials in an analytic form suitable for use within standard quantum chemistry codes. These pseudopotentials are suitable for use within Hartree-Fock and correlated wave function methods, including diffusion quantum Monte Carlo calculations.PACS numbers: 71.15. Dx, 02.70.Ss Pseudopotentials or effective core potentials (ECPs) are commonly used within electronic structure calculations to replace the chemically inert core electrons. The influence of the core on the valence electrons is then described by an angular-momentum-dependent effective potential, leading to greatly improved computational efficiency in ab initio calculations for heavy atoms. The use of pseudopotentials is well established within HartreeFock (HF) and Density Functional Theory (DFT), and in correlated wave function calculations.Our main interest is in diffusion quantum Monte Carlo (DMC) calculations. 1,2 This technique provides an accurate solution of the interacting electron problem for which the computational effort scales with the number of electrons, N , as approximately N 3 , which is better than other correlated wave function approaches. Unfortunately, scaling with atomic number, Z, is approximately 3,4 Z 5−6.5 . The use of a pseudopotential reduces the effective value of Z, making DMC calculations feasible for heavy atoms.There is evidence that HF pseudopotentials give better results within DMC than DFT pseudopotentials. 5 It appears that the complete neglect of core-valence correlation within HF theory leads to better pseudopotentials than the description of core-valence correlation provided by DFT. Moreover, core-valence correlation can be included within correlated wave function calculations performed with HF pseudopotentials by using core polarization potentials. 6,7,8 Core polarization potentials mimic the effects of dynamical polarization of the core by the valence electrons, as well as static polarization effects due to the other ions. We would therefore like to use HF pseudopotentials in our DMC calculations, preferably constructed from Dirac-Fock (DF) theory in order to include the relativistic effects which are significant for heavy atoms.Standard quantum chemistry packages are convenient for generating the "guiding wave functions" required in DMC calculations. We would therefore like our pseudopotentials to be available in the standard parameterized form of a sum of Gaussian functions multiplied by powers of the electron-nucleus separation.Extensive sets of parameterized pseudopotentials are available in the literature, but they have generally been constructed with different goals to ours. Relativistic pseudopotentials 9 generated within DFT and the local density approximation have be...

Electron-hole pair creation by an adsorbate incident on a metal surface is described using ab initio methods. The approach starts with standard first principles electronic structure theory, and proceeds to combine classical, quantum oscillator and time dependent density functional methods to provide a consistent description of the non-adiabatic energy transfer from adsorbate to substrate. Of particular interest is the conservation of the total energy at each level of approximation, and the importance of a spin transition as a function of the adsorbate/surface separation. Results are presented and discussed for H and D atoms incident on the Cu(111) surface.

We report diffusion quantum Monte Carlo calculations of three-dimensional Wigner crystals in the density range rs = 100 to 150. We have tested different types of orbital for use in the approximate wave functions but none improve upon the simple Gaussian form. The Gaussian exponents are optimized by directly minimizing the diffusion quantum Monte Carlo energy. We have carefully investigated and sought to minimize the potential biases in our Monte Carlo results. We conclude that the uniform electron gas undergoes a transition from a ferromagnetic fluid to a body-centered cubic Wigner crystal at rs = 106±1. The diffusion quantum Monte Carlo results are compared with those from Hartree-Fock and Hartree theory in order to understand the role played by exchange and correlation in Wigner crystals. We also study "floating" Wigner crystals and give results for their pair correlation functions.

All-electron variational and diffusion quantum Monte Carlo calculations of the ground state energies of the first row atoms (from Li to Ne) are reported. The authors use trial wave functions of four types: single-determinant Slater-Jastrow wave functions, multideterminant Slater-Jastrow wave functions, single-determinant Slater-Jastrow wave functions with backflow transformations, and multideterminant Slater-Jastrow wave functions with backflow transformations. At the diffusion quantum Monte Carlo level and using their multideterminant Slater-Jastrow wave functions with backflow transformations, they recover 99% or more of the correlation energies for Li, Be, B, C, N, and Ne, 97% for O, and 98% for F.