  The proposed next generation Event Horizon Telescope (ngEHT) concept
envisions the imaging of various astronomical sources on scales of
microarcseconds in unprecedented detail with at least two orders of magnitude
improvement in the image dynamic ranges by extending the Event Horizon
Telescope (EHT). A key technical component of ngEHT is the utilization of large
aperture telescopes to anchor the entire array, allowing the connection of less
sensitive stations through highly sensitive fringe detections to form a dense
network across the planet. Here, we introduce two projects for planned next
generation large radio telescopes in the 2030s on the Chajnantor Plateau in the
Atacama desert in northern Chile, the Large Submillimeter Telescope (LST) and
the Atacama Large Aperture Submillimeter Telescope (AtLAST). Both are designed
to have a 50-meter diameter and operate at the planned ngEHT frequency bands of
86, 230 and 345\,GHz. A large aperture of 50\,m that is co-located with two
existing EHT stations, the Atacama Large Millimeter/Submillimeter Array (ALMA)
and the Atacama Pathfinder Experiment (APEX) Telescope in the excellent
observing site of the Chajnantor Plateau, will offer excellent capabilities for
highly sensitive, multi-frequency, and time-agile millimeter very long baseline
interferometry (VLBI) observations with accurate data calibration relevant to
key science cases of ngEHT. In addition to ngEHT, its unique location in Chile
will substantially improve angular resolutions of the planned Next Generation
Very Large Array in North America or any future global millimeter VLBI arrays
if combined. LST and AtLAST will be a key element enabling transformative
science cases with next-generation millimeter/submillimeter VLBI arrays.
