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Some improvements on pseudopotentials have been made to achieve the optimal computing efficiency in large scale ab initio total energy calculations, which is essential for the fundamental understanding of many complex processes and structures of condensed matter. A computational study of a weakly ordered system is done as an application.A strategy to improve the construction of Optimised Pseudopotentials is proposed. To generate a softer optimised pseudopotential, we use a smaller number of constraints in the minimisation procedure, also we reduce the number of spherical Bessel function terms used to expand pseudowavefunctions. Most importantly, we have introduced a new way to use Qc parameter, which nicely integrates these approaches. In our method, Qc is used as a kinetic energy filter to regulate the shape of a potential. This allows us to generate very well optimised potentials and improves their scattering property. This new pseudopotential scheme has been used in 2p and 3d elements as well as other softer elements, and has proved to provide a very reliable and flexible procedure for generating softer optimised pseudopotentials.We have invented a method to reduce the number of non-local components of pseudopotentials. The benefit of treating pseudopotential this way is significant for large scale ab initio calculations, most importantly in the real-space non-local potential scheme. In addition to the efficiency one can gain from this implementation, being able to eliminate the Kleinman-Bylander projectors of some angular momentum channels of a pseudopotential helps to improve the accuracy of pseudopotential in many cases, especially those needed to use a highly exited-state pseudowavefunction as a reference in constructing its Kleinman-Bylander form.

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