Quantum Monte Carlo ͑QMC͒ calculations are only possible in finite systems and so solids and liquids must be modeled using small simulation cells subject to periodic boundary conditions. The resulting finite-size errors are often corrected using data from local-density functional or Hartree-Fock calculations, but systematic errors remain after these corrections have been applied. The results of our jellium QMC calculations for simulation cells containing more than 600 electrons confirm that the residual errors are significant and decay very slowly as the system size increases. We show that they are sensitive to the form of the model Coulomb interaction used in the simulation cell Hamiltonian and that the usual choice, exemplified by the Ewald summation technique, is not the best. The finite-size errors can be greatly reduced and the speed of the calculations increased by a factor of 20 if a better choice is made. Finite-size effects plague most methods used for extended Coulomb systems and many of the ideas in this paper are quite general: they may be applied to any type of quantum or classical Monte Carlo simulation, to other many-body approaches such as the GW method, and to Hartree-Fock and density-functional calculations.

Objectives. Few studies have specifically tested the Cry of Pain model (Williams, 2001). This model conceptualises suicidal behaviour as a behavioural response to a stressful situation which has three components: defeat, no escape potential, and no rescue. In addition, the model specifies a mediating role for entrapment on the defeatsuicidal ideation relationship, and a moderating role for rescue factors on the entrapment-suicidal ideation relationship. This is the first study to investigate the utility of this psychological model in a sample of first-time and repeat self-harm (SH) patients. Method. One hundred and thirteen patients who had been admitted to hospitalfollowing an episode of SH (36 first-time, 67 repeat) and 37 hospital controls completed measures of defeat, entrapment/escape potential, rescue (social support and positive future thinking), as well as depression, anxiety and suicidal ideation.

A model interaction is introduced for quantum many-body simulations of Coulomb systems using periodic boundary conditions. The interaction gives much smaller finite size effects than the standard Ewald interaction and is also much faster to compute. Variational quantum Monte Carlo simulations of diamond-structure silicon with up to 1000 electrons demonstrate the effectiveness of our method. ͓S0163-1829͑97͒51408-1͔Many-body simulation techniques such as the variational 1 and diffusion 2 quantum Monte Carlo ͑QMC͒ methods are capable of yielding highly accurate results for correlated systems. Large systems are normally modeled using a finite simulation cell subject to periodic boundary conditions. This, however, introduces ''finite size effects'' which are often very important, particularly for systems with long ranged interactions such as the Coulomb interaction. In this paper we introduce a method for dealing with long ranged interactions in quantum many-body simulations which greatly reduces these finite size effects. This method is a generalization of one we developed earlier for homogeneous systems such as jellium. 3 We illustrate our method with variational QMC calculations on diamond-structure silicon. The ideas described in this paper are of wide generality and can be applied to other quantum many-body schemes, such as the HF and ''GW'' ͑Ref. 4͒ methods, and to long ranged interactions other than the Coulomb interaction.The finite size effects encountered in QMC calculations for electronic systems can be divided into two terms: ͑i͒ the independent particle finite size effect ͑IPFSE͒ and ͑ii͒ the Coulomb finite size effect ͑CFSE͒. 3,5 The IPFSE and CFSE are most easily defined with reference to results of local density approximation ͑LDA͒ calculations. The IPFSE is the difference between the LDA energies per atom in the finite and infinite systems and the CFSE is the remainder of the finite size error. Recently we presented a method 6 for reducing the IPFSE in insulating systems by using the ''special k-points'' method borrowed from band-structure theory. 7 This method reduces the IPFSE by an order of magnitude and leaves the CFSE as the dominant finite size effect. The CFSE, which is the subject of this work, arises from the long range of the Coulomb interaction and is therefore of wide significance in many-body simulations.We illustrate the CFSE by comparing the results of LDA and Hartree-Fock calculations. To define the LDA and HF energies for simulation cells with periodic boundary conditions we must specify the form of the model electronelectron interaction used. This interaction acts only between the charges within the simulation cell, but is intended to model the forces that would act in the center of an infinite array of identical copies of that cell. Unfortunately, sums of Coulomb 1/r potentials in extended systems are only conditionally convergent, and hence these forces are not uniquely defined until the boundary conditions at infinity have been specified. It is standard to calculate the potential...

Further research is required to determine memory loss associated with ECT, controlling for the direct effects of the depressive state.

Wave functions for the homogeneous electron gas, a germanium pseudosolid, and a germanium pseudoatom are optimized using the method of variance minimization. Forms for the Jastrow factor which are convenient to optimize and may be evaluated rapidly are devised and tested and we stress the advantages of using expressions which are linear in the variable parameters. For each system studied we have performed variational and diffusion quantum Monte Carlo calculations to test the accuracy of the optimized wave functions. The results of our study are very promising for future applications of quantum Monte Carlo methods to real materials.