We investigate the formation and early evolution of star clusters assuming that they form from a turbulent starless clump of given mass bounded inside a parent self-gravitating molecular cloud characterized by a particular mass surface density .
As a first step we assume instantaneous star cluster formation and gas expulsion .
We draw our initial conditions from observed properties of starless clumps .
We follow the early evolution of the clusters up to 20 Myr , investigating effects of different star formation efficiencies , primordial binary fractions and eccentricities and primordial mass segregation levels .
We investigate clumps with initial masses of M _ { cl } = 3000 \ > { M } _ { \odot } embedded in ambient cloud environments with mass surface densities , \Sigma _ { cloud } = 0.1 and 1 \ > { g\ > cm ^ { -2 } } .
We show that these models of fast star cluster formation result , in the fiducial case , in clusters that expand rapidly , even considering only the bound members .
Clusters formed from higher \Sigma _ { cloud } environments tend to expand more quickly , so are soon larger than clusters born from lower \Sigma _ { cloud } conditions .
To form a young cluster of a given age , stellar mass and mass surface density , these models need to assume a parent molecular clump that is many times denser , which is unrealistic compared to observed systems .
We also show that in these models the initial binary properties are only slightly modified by interactions , meaning that binary properties , e.g. , at 20 Myr , are very similar to those at birth .
With this study we set up the basis of future work where we will investigate more realistic models of star formation compared to this instantaneous , baseline case .